Question

What function do the lipolysyl moieties of the second enzyme in the pyruvate dehydrogenase complex serve?

Answer 1

ANSWER:

The second enzyme of the pyruvate dehydrogenate is the dihydrolipoyl transacetylase.The thioacetate is generated on S1 of lipoate due to the rate limiting reaction of pyruvate dehydrogenase E1 action.

This lipoate thioester functionality is now translocated into dihydrolipoyl transacetylase (E2) active site. And it is this active site of enzyme E2 where a transacetylation reaction transfers the acetyl from the swinging arm of lipoyl to thiol of coenzyme A thus producing acetyl coA. This acetyl CoA is released from the enzyme complex and enters the citric acid cycle. Thus enzyme E2 of pyruvate dehydogenase is also referred to as lipoamylase reductase tracetylase.