Talk:Coenzyme

From Wikipedia, the free encyclopedia

	MCB Portal This article is within the scope of the Molecular and Cellular Biology WikiProject. To participate, visit the WikiProject for more information. The WikiProject's current monthly collaboration is focused on improving Restriction enzyme.
B	This article has been rated as B-Class on the assessment scale.
High	This article is on a subject of High-importance within molecular and cellular biology.
Article Grading: The following comments were left by the quality and importance raters: (edit · history · refresh · how to use this template) Article should include how this affects human experience. Everyone is selling pills out there but is it useless as a supplement??

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.

To-do list for Coenzyme:	edit · history · watch · refresh
Here are some tasks you can do: Expand: Expand the Introduction. Give more examples of co-enzymes. Create a section showing how the co-enzyme mechanism works.

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)

I'd say that biotin and cyanocobalamin are cofactors rather than coenzymes, since they are not released from enzymes as part of the normal catalytic cycle. Ascorbic acid probably does fit the definition though. Tim Vickers (talk) 16:59, 19 November 2007 (UTC)

I am not sure that definition of coenzyme in the lead is correct. The cited Glossary tells the following:

• Coenzyme.

"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."

• Cofactor

"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)

After all, I guess, "coenzymes" and "cofactors" are the same since they all are involved in enzymatic reactions, including electron transfer and isomerization. However, those of them who are covalently (not "tightly") bound to proteins are called "prostetic groups" (a sub-group of coenzymes/cofactors).Biophys (talk) 18:13, 28 November 2007 (UTC)

I would tell that most common and useful term is "cofactor", while word "coenzyme" is traditionally (and rather arbitrary) used for several vitamine-derived organic cofactors, such as Coenzyme Q, Coenzyme A and Coenzyme B12. Actually, we should focus more on article Cofactor.Biophys (talk) 18:31, 28 November 2007 (UTC)

I have always hated how loose these terms are. My preferred definition is that a coenzyme is a molecule that accepts or donates a chemical group in an enzyme reaction and is released as part of the normal catalytic cycle. The difference between a coenzyme and regular substrates is that coenzymes are used by multiple different types of enzyme to donate the same chemical group - they are general group transfer reagents. Tim Vickers (talk) 19:28, 28 November 2007 (UTC)

That is true. But main problem is this: you are trying to distinguish "coenzymes" and "cofactors" as two different classes of molecules (partly based on a misleading definition in the glossary), however "coenzymes" seem to be usually treated as a small sub-group of "cofactors" in the scientific literature if I understand this correctly. Biophys (talk) 17:06, 29 November 2007 (UTC)

The problem is that there is little consistency in the scientific literature. As the article notes, these terms are commonly used very loosely. When I wrote this I therefore used a specific and clear definition from IUPAC - the most reliable source I could find. I've tried rewriting the lead to make the sub-classifications more clear. Tim Vickers (talk) 17:19, 29 November 2007 (UTC)

I think you fixed this problem in new version of the article. It is much better!Biophys 00:15, 1 December 2007 (UTC)

[edit] FAD and FMN?

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)