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What is the relationship between ATP recycling and coenzymes ? ATP is no coenzyme !!
Lulubou ( talk) 12:46, 6 March 2009 (UTC)
Thiamine is a vitamine and thiamine diphosphate is definitely a cofactor and should be in the list. Therefore I added it again. Narayanese, why did you undo my previous addition of thiamine ? —Preceding unsigned comment added by 139.165.98.37 ( talk) 12:42, 6 March 2009 (UTC) Lulubou ( talk) 12:44, 6 March 2009 (UTC)
For teaching biochemistry for years I know that it is not easy to escape contradictions when talking about coenzymes and cofactors. The best way to do would be to unit the articles on cofactors and coenzymes (call it "Cofactors and coenzymes). Cofactors are the general term comprising coenzymes (organic molecules with enzymatic function) and metal factors. Some of these are prosthetic groups with enzymatic function (FAD, heme for instance). But some prosthetic groups (tightly bound non proteinic groups such as sugars or lipid) are not necessarily cofactors. For me, ATP is certainly none of these (it has no catalytic function, in constrast to NAD, and it is not a prosthetic group): it is a plain substrate, though you can call it an activated carrier of phosphate if you wish. The important point is the relationship between B vitamin and coenzymes (TPP, NAD, FAD, lipoamide ...).
Each of these coenzymes represents a case of its own: some are recycled immediately such as FAD or lipoamide, others in a second reaction (NAD, TPP). Some bind to the enzyme only during the reaction (NAD). Some are tightly, but not covalently bound (thiamine pryphosphate in transketolase very tightly, reversibly in pyruvate dehydrogenase), some are covalently bound (FAD, lipoamide).
"Prosthetic group" is a very general term, independent of enzymatic function: it can be RNA, sugars, phosphate, lipids, without enzymatic function or FAD, hemes, metals with enymatic function.
Lehninger (Biochemistry, the molecular basis of cell structure and function, 1975, Worth publishers) considered that coenzymes are: thiamine pyrophosphate, FMN, FAD, NAD, CoA, pyrodoxalphosphate, biotine, tetrahydrofolic acid, lipoic acid, cobalamine
Stryer (Biochemistry, 4th edition, 1995, W. H. Freeman and Company, New York). Lists coenzymes (Table 17.3, page 453): thiamine pyrophosphate, FMN, FAD, NAD, pyridoxal phosphate, Coenzyme A, Biotin, tetrahydrofolate, cobalamine
Both textbooks do not mention the word "cofactor".
Rawn (Biochemistry, 1989, Neil Paterson Publishers, Burlington, North Carolina) does not give a clear definition of "coenzyme", but calls FAD (page 340), thiamine pyrophosphate and lipoamide (page 333) all coenzymes.
Matthews and Van Holde (Biochemistry, 2nd edition, 1995, The Benjamin/Cummings publishing company, Menlo Park, California) lists in "coenzymes" : NAD, FAD, thiamine pyrophosphate, Coenzyme A, Biotin, pyridoxal phosphate (page 390)
Harper (Harper's Biochemistry, 2nd edition, 1990, Prentice Hall) has an even broader definition of coenzymes insofar as he defines them as cosubstrates. He includes sugar phosphates, CoA, thiamine pyrophosphate, pyridoxal phosphate, folate, biotin, cobalamine, lipoic acide, NAD, FMN, FAD, coenzyme Q
On Monday I have to check in more recent text books in my office.
You can also look in "Jordan F.Nat Prod Rep. 2003 Apr;20(2):184-201. Current mechanistic understanding of thiamin diphosphate-dependent enzymatic reactions." who calls thiamine diphosphate a coenzyme. I agree, that in the primary literature the term cofactor is also used for thiamine diphosphate, but as it is the more general term it does not exclude it to be also a coenzyme.
Cofactor, coenzyme and prosthetic group represent three different sometimes overlapping concepts:
In "coenzyme" the emphasis is on the suffix "enzyme": an organic molecule participating in the enzymatic mechanism of an enzyme. It can be tightly bound or not, recycled in the same reaction or not.
"Cofactor" designates an organic (coenzyme) or an inorganic (metal) factor required for enzyme activity.
"Prosthetic group" is a factor (organic or not) that is tightly bound to an apoprotein (enzyme or structural protein) - in contrast to coenzyme and cofactor no relation to enzyme activity
Presented like this, there is no contradiction and IT MATCHES THE SCIENTIFIC LITERATURE !!!
I think that the best way to do is to unite the three concepts in only one article, referring to articles for the individual compounds (NAD, FAD, thiamine pyrophosphate, glycoprotein, lipoiproteins,...). The way it is now is totally confusing.
I am totally willing to collaborate in your effort to make it nice and comprehensive. Lulubou ( talk) 10:25, 8 March 2009 (UTC)
Lulubou ( talk) 10:28, 8 March 2009 (UTC)
See also:
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/coenzy_.htm
http://www.elmhurst.edu/~chm/vchembook/571cofactor.html
http://www.molecular-plant-biotechnology.info/enzyme-technology/coenzymes-and-cofactors.htm
http://www.microbiologyprocedure.com/enzymes-isozymes-coenzymes/coenzymes-cofactors.htm
http://www.webpages.uidaho.edu/~dcole/Topic%207_Vitamins.pdf
http://www.chem.qmul.ac.uk/iupac/misc/B6.html
http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1179624&pageindex=1#page
By the way, a metal ion can be a prosthetic group (tightly bound Cu+ in the repiratory chain) or not (reversibly bound Mg2+ in kinase reactions).
Lulubou ( talk) 13:33, 8 March 2009 (UTC)
YES Pyridoxal phosphate is a prothetic group and a coenzyme : there is no contradictiion in this. Lulubou ( talk) 21:24, 8 March 2009 (UTC)
Due to this chronic confusion over if these terms have any fixed meaning, I'm certainly open to the idea of merging the pages
prosthetic group and
coenzyme into the top-level article
Cofactor (biochemistry). I don't think the resulting article would be of unmanageable size, which would be the major concern. An alternative is to note in the introductions of the three separate articles that the terms are often used loosely and interchangeably. What I would be unhappy with would having three articles with redundant content - for example having TPP and FMN listed both here as coenzymes and also listed as
prosthetic groups in a different article.
Tim Vickers (
talk)
20:37, 8 March 2009 (UTC)
I can't help it. All the textbooks agree that FMN is a coenzyme AND a prosthetic group. As both terms designate different properties (functional for the first and structural for the second) there is no contradiction.
Lulubou ( talk) 15:45, 9 March 2009 (UTC)
The notions of prosthetic group and coenzyme are independent:
A prosthetic group is a non proteinic group associated with an apoprotein, the two forming a heteroprotein. Thus immunoglobulins having no enzymatic activity, contain covalently bound sugars that form a prosthetic group. I surely agree that pyridoxal phosphate as a coenzyme involved in enzymatic acitivity.
I am just saying that prosthetic group are non proteinic groups of many proteins, enzymes and structural proteins. It happens that some prosthetic gropus (pyridoxal phosphate, FAD...) have a coenzyme function.
The notions of prosthethic group and coenzyme are different concepts that can be overlapping.
FAD, pyridoxal phosphate: coenzymes and prosthetic groups
NAD: a coenzyme but not a prosthetic group
Sugars in glycoproteins: prosthetic groups but not coenzymes
Lulubou ( talk) 21:24, 8 March 2009 (UTC)
As promised, here are more recent definitions of "coenzymes":
Metzler DE, (2001) Biochemistry. The chemical reactions of living cells, 2nd edition, Harcourt, San Diego.
On page 719 :
« Coenzymes are non protein molecules that function as essential parts of enzymes.... ...Very tightly bound coenzyme groups are often called prosthetic groups, but there is no sharp line that divides prosthetic groups from the loosely bound coenzymes. »
This is exactly my opinion.
He distinguishes three kinds of coenzymes :
° High group transfer potential such as ATP and GTP, but he states that ATP can also be regarded as substrate
° Derivatives of vitamins such as coenzyme A, pyridoxal phosphate, thiamine diphosphate, vitamin B12
° Oxidative coenzymes
A similar definition can be found in :
Lehninger. Principles of Biochemistry, Nelson DL and Cox M.M. (2000), 3rd edition, Worth Publishers, New York – page 245
They list as coenzymes Biocytin, Coenzyme A, Cobalamine, FAD, lipoate, NAD, pyridixal phosphate, tetrahydrofolat, and thiamine pyrophosphate
Finally :
Campbell and Farrell (2009) Biochemistry, Student Edition, They do not give a clear definition of coenzyme. They call it « a mixed bag of organic compounds ; many of them are vitamins or are metabolically related to vitamins » (page 194) They list as coenzymes : Biotin, coenzyme A, flavin coenzymes, lipoic acid, nicotinamide adenine nucleotides, pyridoxal phosphate, tetrahydrofolic acid and thiamine pyrophosphate.
Are these enough references for you, Narayanese ?
By the way, I found a clear stupidity in the article on "cofactor", with a figure showing "the bound "heme" cofactor of succinate dehydrogenase..." Succinate dehydrogenase is is the typical textbook example of a oxidoreductase of the respiratory chain that is NOT a heme protein but an iron-sulfur protein. This can be found in any textbook. Lulubou ( talk) 09:35, 9 March 2009 (UTC)
Succinate dehydrogenase contains three different iron sulfur clusters and one covalently bound FAD: no heme! The protein you refer to is a small heme (cytochrome b560) binding protein belonging to succinate-ubiquinone reductase (complex II) and that is associated with succinate dehydrogenase. Thus the cristallographic structure shown is that of this small subunit (or anchoring protein) but not of succinate dehydrogenase.
http://www.ncbi.nlm.nih.gov/pubmed/1447196?ordinalpos=13&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum http://www.wikigenes.org/e/ref/e/1447196.html
Concerning the eternal distinction between prosthetic groups and coenzymes, I think that we should stick to the biochemical textbooks (that are the reference also for students), and I did not find one that opposes the terms coenzyme and prosthetic groups. They all consider that a coenzyme is an organic molecule loosely or tightly bound.
Consider cofactors as NAD+ or thiamine diphosphate that in some cases are loosely bound and in some cases tightly. Will you consider that in the first case they are coenzyme and in the second cofactor ? You are not out of difficulty. I changed the three articles on cofactors, coenzyme (this one could be fused with the cofactor article) and prosthetic groups in a way that they seem coherent (at least to me) and without contradiction. My main claim is that cofactors (coenzymes ) and prosthetic groups are based on different concepts (function or structure). This way you avoid many problems and you are coherent with text books. Do not forget that the notion of prosthetic group also encompasses groups (sugars, lipids...) that are not coenzymes. If you keep the previous difinition (prosthetic groups are different from coenzymes) that means that the only term to designate a "tightly bound cofactor important for catalysis" is the term "prosthetic group". But this term has a much broader definition (any non amino acids part of any protein). You will again run in trouble, as prosthetic group will take different meanings according to what you are talking about. Another way out would be to invent a new name to designate a "tightly bound cofactor important for catalysis" and oppose it to the term "coenzyme" and include it in the prosthetic group family. But first you have to get this accepted in the primary literature. Good luck !!
Lulubou ( talk) 18:18, 9 March 2009 (UTC)
I agree that it will very difficult to eliminate all contradictions. For instance I would never call a heme a coenzyme. But why ? In general the term coenzyme is limited to vitamin derivatives (NAD, FAD, thiamine pyrophosphate, pyridoxal phosphate, coenzyme A...)
Concerning prosthetic groups and coenzymes, look at these addresses:
http://www.chemistryexplained.com/Ce-Co/Coenzyme.html http://www.biologie.uni-hamburg.de/b-online/e19/19b.htm http://www.encyclopedia.com/doc/1O39-prostheticgroup.html http://fixedreference.org/en/20040424/wikipedia/Coenzyme http://www1.cleveland.edu/uploads/Bracho/CHE%20568%20UNIT%209.pdf
I have to check if I find something in the primary scientific literature. I would certainly like to write an update on this problem.
I think that your idea of mentioning the existence of opposing view points is good. Can I leave it to you ?
Lulubou ( talk) 20:45, 9 March 2009 (UTC)
The distinction (if there is one) between the reduced and oxidized form of a coenzyme could be made more clear. For example - is ATP or ADP referred to as the coenzyme? Is NAD+ or is NADH the coenzyme? Dryphi ( talk) 17:05, 4 July 2008 (UTC)
Arcadian removed Ascorbic acid, Biotin, and Cyanocobalamin from the list of vitamin derived coenzymes. Is there any reason why these shouldn't be on the list? Stable attractor ( talk) 07:08, 19 November 2007 (UTC)
"A low-molecular-weight, non-protein organic compound (often a nucleotide) participating in enzymatic reactions as dissociable acceptor or donor of chemical groups or electrons."
"An organic molecule or ion (usually a metal ion) that is required by an enzyme for its activity. It may be attached either loosely (coenzyme) or tightly (prosthetic group)."
That is correct. But it means that "coenzyme" is simply a "cofactor" which is involved in chemical reactions, including electron transfer (!), as I have always thought. However, glossary definition above tells than not every chemical reaction qualify. It tells: "dissociable acceptor or donor of chemical groups or electrons". Hence a cofactor such as retinal, which undergoes an isomerization (a photochemical reaction), would not qualify as a "coenzyme"? Is that right? Biophys ( talk) 17:48, 28 November 2007 (UTC)
Or maybe "coenzyme" is any "cofactor" that is loosely attched to a protein? That would be different. That would mean that retinal is a "prostetic group" in bacteriorhodopsin, and who knows what in rhodopsin. Biophys ( talk) 18:00, 28 November 2007 (UTC)
I think these should be classified as prosthetic groups. Flavoenzymes bind their cofactor quite tightly. Can anybody think of any reactions where a free flavin is a substrate? Tim Vickers 21:46, 1 December 2007 (UTC)
The comment(s) below were originally left at Talk:Coenzyme/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
Article should include how this affects human experience. Everyone is selling pills out there but is it useless as a supplement?? |
Last edited at 21:55, 1 June 2007 (UTC). Substituted at 05:08, 13 May 2016 (UTC)
![]() | This redirect does not require a rating on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
![]() | This article was the
MCB Collaboration of the Month for the month of November 2007. For more details, see the
MCB Collaboration of the Month history. |
What is the relationship between ATP recycling and coenzymes ? ATP is no coenzyme !!
Lulubou ( talk) 12:46, 6 March 2009 (UTC)
Thiamine is a vitamine and thiamine diphosphate is definitely a cofactor and should be in the list. Therefore I added it again. Narayanese, why did you undo my previous addition of thiamine ? —Preceding unsigned comment added by 139.165.98.37 ( talk) 12:42, 6 March 2009 (UTC) Lulubou ( talk) 12:44, 6 March 2009 (UTC)
For teaching biochemistry for years I know that it is not easy to escape contradictions when talking about coenzymes and cofactors. The best way to do would be to unit the articles on cofactors and coenzymes (call it "Cofactors and coenzymes). Cofactors are the general term comprising coenzymes (organic molecules with enzymatic function) and metal factors. Some of these are prosthetic groups with enzymatic function (FAD, heme for instance). But some prosthetic groups (tightly bound non proteinic groups such as sugars or lipid) are not necessarily cofactors. For me, ATP is certainly none of these (it has no catalytic function, in constrast to NAD, and it is not a prosthetic group): it is a plain substrate, though you can call it an activated carrier of phosphate if you wish. The important point is the relationship between B vitamin and coenzymes (TPP, NAD, FAD, lipoamide ...).
Each of these coenzymes represents a case of its own: some are recycled immediately such as FAD or lipoamide, others in a second reaction (NAD, TPP). Some bind to the enzyme only during the reaction (NAD). Some are tightly, but not covalently bound (thiamine pryphosphate in transketolase very tightly, reversibly in pyruvate dehydrogenase), some are covalently bound (FAD, lipoamide).
"Prosthetic group" is a very general term, independent of enzymatic function: it can be RNA, sugars, phosphate, lipids, without enzymatic function or FAD, hemes, metals with enymatic function.
Lehninger (Biochemistry, the molecular basis of cell structure and function, 1975, Worth publishers) considered that coenzymes are: thiamine pyrophosphate, FMN, FAD, NAD, CoA, pyrodoxalphosphate, biotine, tetrahydrofolic acid, lipoic acid, cobalamine
Stryer (Biochemistry, 4th edition, 1995, W. H. Freeman and Company, New York). Lists coenzymes (Table 17.3, page 453): thiamine pyrophosphate, FMN, FAD, NAD, pyridoxal phosphate, Coenzyme A, Biotin, tetrahydrofolate, cobalamine
Both textbooks do not mention the word "cofactor".
Rawn (Biochemistry, 1989, Neil Paterson Publishers, Burlington, North Carolina) does not give a clear definition of "coenzyme", but calls FAD (page 340), thiamine pyrophosphate and lipoamide (page 333) all coenzymes.
Matthews and Van Holde (Biochemistry, 2nd edition, 1995, The Benjamin/Cummings publishing company, Menlo Park, California) lists in "coenzymes" : NAD, FAD, thiamine pyrophosphate, Coenzyme A, Biotin, pyridoxal phosphate (page 390)
Harper (Harper's Biochemistry, 2nd edition, 1990, Prentice Hall) has an even broader definition of coenzymes insofar as he defines them as cosubstrates. He includes sugar phosphates, CoA, thiamine pyrophosphate, pyridoxal phosphate, folate, biotin, cobalamine, lipoic acide, NAD, FMN, FAD, coenzyme Q
On Monday I have to check in more recent text books in my office.
You can also look in "Jordan F.Nat Prod Rep. 2003 Apr;20(2):184-201. Current mechanistic understanding of thiamin diphosphate-dependent enzymatic reactions." who calls thiamine diphosphate a coenzyme. I agree, that in the primary literature the term cofactor is also used for thiamine diphosphate, but as it is the more general term it does not exclude it to be also a coenzyme.
Cofactor, coenzyme and prosthetic group represent three different sometimes overlapping concepts:
In "coenzyme" the emphasis is on the suffix "enzyme": an organic molecule participating in the enzymatic mechanism of an enzyme. It can be tightly bound or not, recycled in the same reaction or not.
"Cofactor" designates an organic (coenzyme) or an inorganic (metal) factor required for enzyme activity.
"Prosthetic group" is a factor (organic or not) that is tightly bound to an apoprotein (enzyme or structural protein) - in contrast to coenzyme and cofactor no relation to enzyme activity
Presented like this, there is no contradiction and IT MATCHES THE SCIENTIFIC LITERATURE !!!
I think that the best way to do is to unite the three concepts in only one article, referring to articles for the individual compounds (NAD, FAD, thiamine pyrophosphate, glycoprotein, lipoiproteins,...). The way it is now is totally confusing.
I am totally willing to collaborate in your effort to make it nice and comprehensive. Lulubou ( talk) 10:25, 8 March 2009 (UTC)
Lulubou ( talk) 10:28, 8 March 2009 (UTC)
See also:
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/coenzy_.htm
http://www.elmhurst.edu/~chm/vchembook/571cofactor.html
http://www.molecular-plant-biotechnology.info/enzyme-technology/coenzymes-and-cofactors.htm
http://www.microbiologyprocedure.com/enzymes-isozymes-coenzymes/coenzymes-cofactors.htm
http://www.webpages.uidaho.edu/~dcole/Topic%207_Vitamins.pdf
http://www.chem.qmul.ac.uk/iupac/misc/B6.html
http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1179624&pageindex=1#page
By the way, a metal ion can be a prosthetic group (tightly bound Cu+ in the repiratory chain) or not (reversibly bound Mg2+ in kinase reactions).
Lulubou ( talk) 13:33, 8 March 2009 (UTC)
YES Pyridoxal phosphate is a prothetic group and a coenzyme : there is no contradictiion in this. Lulubou ( talk) 21:24, 8 March 2009 (UTC)
Due to this chronic confusion over if these terms have any fixed meaning, I'm certainly open to the idea of merging the pages
prosthetic group and
coenzyme into the top-level article
Cofactor (biochemistry). I don't think the resulting article would be of unmanageable size, which would be the major concern. An alternative is to note in the introductions of the three separate articles that the terms are often used loosely and interchangeably. What I would be unhappy with would having three articles with redundant content - for example having TPP and FMN listed both here as coenzymes and also listed as
prosthetic groups in a different article.
Tim Vickers (
talk)
20:37, 8 March 2009 (UTC)
I can't help it. All the textbooks agree that FMN is a coenzyme AND a prosthetic group. As both terms designate different properties (functional for the first and structural for the second) there is no contradiction.
Lulubou ( talk) 15:45, 9 March 2009 (UTC)
The notions of prosthetic group and coenzyme are independent:
A prosthetic group is a non proteinic group associated with an apoprotein, the two forming a heteroprotein. Thus immunoglobulins having no enzymatic activity, contain covalently bound sugars that form a prosthetic group. I surely agree that pyridoxal phosphate as a coenzyme involved in enzymatic acitivity.
I am just saying that prosthetic group are non proteinic groups of many proteins, enzymes and structural proteins. It happens that some prosthetic gropus (pyridoxal phosphate, FAD...) have a coenzyme function.
The notions of prosthethic group and coenzyme are different concepts that can be overlapping.
FAD, pyridoxal phosphate: coenzymes and prosthetic groups
NAD: a coenzyme but not a prosthetic group
Sugars in glycoproteins: prosthetic groups but not coenzymes
Lulubou ( talk) 21:24, 8 March 2009 (UTC)
As promised, here are more recent definitions of "coenzymes":
Metzler DE, (2001) Biochemistry. The chemical reactions of living cells, 2nd edition, Harcourt, San Diego.
On page 719 :
« Coenzymes are non protein molecules that function as essential parts of enzymes.... ...Very tightly bound coenzyme groups are often called prosthetic groups, but there is no sharp line that divides prosthetic groups from the loosely bound coenzymes. »
This is exactly my opinion.
He distinguishes three kinds of coenzymes :
° High group transfer potential such as ATP and GTP, but he states that ATP can also be regarded as substrate
° Derivatives of vitamins such as coenzyme A, pyridoxal phosphate, thiamine diphosphate, vitamin B12
° Oxidative coenzymes
A similar definition can be found in :
Lehninger. Principles of Biochemistry, Nelson DL and Cox M.M. (2000), 3rd edition, Worth Publishers, New York – page 245
They list as coenzymes Biocytin, Coenzyme A, Cobalamine, FAD, lipoate, NAD, pyridixal phosphate, tetrahydrofolat, and thiamine pyrophosphate
Finally :
Campbell and Farrell (2009) Biochemistry, Student Edition, They do not give a clear definition of coenzyme. They call it « a mixed bag of organic compounds ; many of them are vitamins or are metabolically related to vitamins » (page 194) They list as coenzymes : Biotin, coenzyme A, flavin coenzymes, lipoic acid, nicotinamide adenine nucleotides, pyridoxal phosphate, tetrahydrofolic acid and thiamine pyrophosphate.
Are these enough references for you, Narayanese ?
By the way, I found a clear stupidity in the article on "cofactor", with a figure showing "the bound "heme" cofactor of succinate dehydrogenase..." Succinate dehydrogenase is is the typical textbook example of a oxidoreductase of the respiratory chain that is NOT a heme protein but an iron-sulfur protein. This can be found in any textbook. Lulubou ( talk) 09:35, 9 March 2009 (UTC)
Succinate dehydrogenase contains three different iron sulfur clusters and one covalently bound FAD: no heme! The protein you refer to is a small heme (cytochrome b560) binding protein belonging to succinate-ubiquinone reductase (complex II) and that is associated with succinate dehydrogenase. Thus the cristallographic structure shown is that of this small subunit (or anchoring protein) but not of succinate dehydrogenase.
http://www.ncbi.nlm.nih.gov/pubmed/1447196?ordinalpos=13&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum http://www.wikigenes.org/e/ref/e/1447196.html
Concerning the eternal distinction between prosthetic groups and coenzymes, I think that we should stick to the biochemical textbooks (that are the reference also for students), and I did not find one that opposes the terms coenzyme and prosthetic groups. They all consider that a coenzyme is an organic molecule loosely or tightly bound.
Consider cofactors as NAD+ or thiamine diphosphate that in some cases are loosely bound and in some cases tightly. Will you consider that in the first case they are coenzyme and in the second cofactor ? You are not out of difficulty. I changed the three articles on cofactors, coenzyme (this one could be fused with the cofactor article) and prosthetic groups in a way that they seem coherent (at least to me) and without contradiction. My main claim is that cofactors (coenzymes ) and prosthetic groups are based on different concepts (function or structure). This way you avoid many problems and you are coherent with text books. Do not forget that the notion of prosthetic group also encompasses groups (sugars, lipids...) that are not coenzymes. If you keep the previous difinition (prosthetic groups are different from coenzymes) that means that the only term to designate a "tightly bound cofactor important for catalysis" is the term "prosthetic group". But this term has a much broader definition (any non amino acids part of any protein). You will again run in trouble, as prosthetic group will take different meanings according to what you are talking about. Another way out would be to invent a new name to designate a "tightly bound cofactor important for catalysis" and oppose it to the term "coenzyme" and include it in the prosthetic group family. But first you have to get this accepted in the primary literature. Good luck !!
Lulubou ( talk) 18:18, 9 March 2009 (UTC)
I agree that it will very difficult to eliminate all contradictions. For instance I would never call a heme a coenzyme. But why ? In general the term coenzyme is limited to vitamin derivatives (NAD, FAD, thiamine pyrophosphate, pyridoxal phosphate, coenzyme A...)
Concerning prosthetic groups and coenzymes, look at these addresses:
http://www.chemistryexplained.com/Ce-Co/Coenzyme.html http://www.biologie.uni-hamburg.de/b-online/e19/19b.htm http://www.encyclopedia.com/doc/1O39-prostheticgroup.html http://fixedreference.org/en/20040424/wikipedia/Coenzyme http://www1.cleveland.edu/uploads/Bracho/CHE%20568%20UNIT%209.pdf
I have to check if I find something in the primary scientific literature. I would certainly like to write an update on this problem.
I think that your idea of mentioning the existence of opposing view points is good. Can I leave it to you ?
Lulubou ( talk) 20:45, 9 March 2009 (UTC)
The distinction (if there is one) between the reduced and oxidized form of a coenzyme could be made more clear. For example - is ATP or ADP referred to as the coenzyme? Is NAD+ or is NADH the coenzyme? Dryphi ( talk) 17:05, 4 July 2008 (UTC)
Arcadian removed Ascorbic acid, Biotin, and Cyanocobalamin from the list of vitamin derived coenzymes. Is there any reason why these shouldn't be on the list? Stable attractor ( talk) 07:08, 19 November 2007 (UTC)
"A low-molecular-weight, non-protein organic compound (often a nucleotide) participating in enzymatic reactions as dissociable acceptor or donor of chemical groups or electrons."
"An organic molecule or ion (usually a metal ion) that is required by an enzyme for its activity. It may be attached either loosely (coenzyme) or tightly (prosthetic group)."
That is correct. But it means that "coenzyme" is simply a "cofactor" which is involved in chemical reactions, including electron transfer (!), as I have always thought. However, glossary definition above tells than not every chemical reaction qualify. It tells: "dissociable acceptor or donor of chemical groups or electrons". Hence a cofactor such as retinal, which undergoes an isomerization (a photochemical reaction), would not qualify as a "coenzyme"? Is that right? Biophys ( talk) 17:48, 28 November 2007 (UTC)
Or maybe "coenzyme" is any "cofactor" that is loosely attched to a protein? That would be different. That would mean that retinal is a "prostetic group" in bacteriorhodopsin, and who knows what in rhodopsin. Biophys ( talk) 18:00, 28 November 2007 (UTC)
I think these should be classified as prosthetic groups. Flavoenzymes bind their cofactor quite tightly. Can anybody think of any reactions where a free flavin is a substrate? Tim Vickers 21:46, 1 December 2007 (UTC)
The comment(s) below were originally left at Talk:Coenzyme/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
Article should include how this affects human experience. Everyone is selling pills out there but is it useless as a supplement?? |
Last edited at 21:55, 1 June 2007 (UTC). Substituted at 05:08, 13 May 2016 (UTC)