Question

?-ketogluterate dehydrogenase and pyruvate dehydrogenase catalyze similar reactions using the same reaction mechanisms. E1 and E2 of the two enzyme complexes share a lot of similarities, however they are not identical. The E3 enzyme of the two enzyme complexes are identical. Keeping the functions of each of the three enzymes in mind, explain why it makes sense that the E1/E2 enzymes are only similar, whereas the E3 enzymes are identical.

Answer 1

Ans.Alpha ketoglutarate dehydrogenase and pyruvate dehydrogenase catalyze similar reactions.They consists three enzymes subunits E1,E2,E3. Out of these 3 enzyme subunits 2 are similar but not identical because in E1 subunit of pyruvate dehydrogenase pyruvate is used as substrate but in case of alpha ketoglutarate the substrate is alpha ketoglutarate but both produces CO2 ,thus they are similar ,but not identical.

Like that for E2 in pyruvate dehydrogenase Acetyl CO-A is produced but,in case of alpha ketoglutarate succinyl CO-A is produced,but both uses Co-SH.thus they are similar but not identical.

But, in case of E3 subnit of both enzymes uses NAD+ and produces NADH+H+. Thus,the E3 subunit in both enzymes is identical enough.in both E3 comes into play when only hydrogen left and all rest of the substrate has been disposed off.