I was thinking about enzyme catalysis, and it seems like enzymes can only catalyse one kind of forward/reverse reaction (please correct me if I am wrong). Does there exist an enzyme that can catalyse multiple reactions with different cofactors? For example, an oxidoreductase that has $Fe(III)$ as a cofactor for one reaction and $H_2O_2$ as a cofactor for another reaction.

  • $\begingroup$ IMO very, very rare, but you may want to look into the case of xanthine dehydrogenase/oxidase. $\endgroup$ – user1136 Sep 16 '19 at 20:08
  • $\begingroup$ Can you name an enzyme for which hydrogen peroxide is a cofactor, rather than a a substrate? How much do you know about enzyme catalysis? $\endgroup$ – David Sep 16 '19 at 22:29
  • $\begingroup$ @user1136, thank you! $\endgroup$ – DS2019 Sep 17 '19 at 22:53
  • $\begingroup$ @David, I am not very familiar with enzyme catalysis-just the basics. I was just curious if there existed such an enzyme. $\endgroup$ – DS2019 Sep 17 '19 at 22:54
  • $\begingroup$ But what you mean by “such” an enzyme is unclear if you are confusing substrate, cofactor and catalytic mechanism. Until you clarify your question it is valueless in relation to the objectives of this site. $\endgroup$ – David Sep 18 '19 at 18:29

It sounds like you are asking about what are commonly referred to as "multifunctional enzymes".

For a reasonably recent article covering this subject — see: Cheng, X. Y., Huang, W. J., Hu, S. C., Zhang, H. L., Wang, H., Zhang, J. X., ... & Ji, Z. L. (2012). A global characterization and identification of multifunctional enzymes. PloS one, 7(6), e38979.

A specific example of such an enzyme is the fatty-acyl-CoA synthase from yeast — this enzyme catalyzes multiple reaction steps that use both NADP and Coenzyme A and also uses a third cofactor, FMN.

The enzyme from yeasts (Ascomycota and Basidiomycota) is a multi-functional protein complex composed of two subunits. One subunit catalyses the reactions EC, 3-oxoacyl-[acyl-carrier-protein] reductase and EC, 3-oxoacyl-[acyl-carrier-protein] synthase, while the other subunit catalyses the reactions of EC, [acyl-carrier-protein] S-acetyltransferase, EC, [acyl-carrier-protein] S-malonyltransferase, EC, 3-hydroxypalmitoyl-[acyl-carrier-protein] dehydratase, EC, enoyl-[acyl-carrier-protein] reductase (NADPH, Si-specific) and EC, (R)-3-hydroxyacid ester dehydrogenase. The enzyme differs from the animal enzyme (EC in that the enoyl reductase domain requires FMN as a cofactor, and the ultimate product is an acyl-CoA (usually palmitoyl-CoA) instead of a free fatty acid.

Source: https://www.ebi.ac.uk/intenz/query?cmd=SearchEC&ec=

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    $\begingroup$ But my reading of the question is that the poster is not thinking of what are in effect multi-enzyme complexes. I suspect from the mention of cofactors in the question that the poster is quite naive. I seem to have heard of enzymes that can change the reaction catalysed in certain circumstances, but two cofactors — unlikely, given their need for specific binding sites. $\endgroup$ – David Sep 16 '19 at 22:26
  • $\begingroup$ @tyersome, that is interesting! I understand that multiple functions would need multiple domains. Thank you for your help! $\endgroup$ – DS2019 Sep 17 '19 at 22:55

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