Kreb's Cycle (TCA): Why H2O Needed in Isomerisation Step?

[Suraj M]

In the isomerisation step of Krebs cycle, the second last step in regeneration. there is a change form fumaric acid to Malic acid by Fumarase. My textbook says that H2O is also added. From chemistry I know that that Malic and Fumaric acid are sterioisomers, Then why need that H2O??

 

[epenguin]

You are confusing malic and and maleic?

 

[Suraj M]

Oh I did not know they were two different compounds! So Maleic acid and fumaric acid are isomers and Malic acid has 2H and 1O extra! Got it thanks!

 

[epenguin]

Oh I did not know they were two different compounds! So Maleic acid and fumaric acid are isomers and Malic acid has 2H and 1O extra! Got it thanks!

The formulae should be spelt out in whatever text you are using. I think it is rather unsatisfactory that all these 'trivial names' for the various carboxylic acids are suddenly just thrown at students coming to the TCA cycle as if they were known, whereas they will never have met them before. Semi-systematic names - e.g. if they were all like alpha-keto-glutarate - would be better IMO.

As I see you are a frequent poster at this site, I will hopefully come back in the next few days with some other considerations about the TCA cycle you might find useful.

 

[Suraj M]

Thank you epenguin