Question

Although the pyruvate dehydrogenase complex is subject io allosteric control, especially inhibition by reaction products, the main regulatory process controlling the enzymes activity in eukaryotes is
A. high energy charge switches the pyruvate dehydrogenase complex on.
B. phosphorylation by ATP that turns on the complex and dephosphorylation that turns it off.
C. phosphorylation by ATP that turns off the complex and dephosphorylation that turns it on.
D. exchange of ADP and ATP on the pyruvate dehydrogenase complex.
E. reversibility of the formation of acetyl CoA from pyruvate.

Answer 1

Answer: C

Explanation:

Pyruvate dehydrogenase complex (PDH) is covalently modified by phosphorylation by PDH kinase and dephosphorylation by PDH phosphatase.

The dephosphorylated form of the enzyme is active. Hence activators of PDH kinase like ATP, NADH and acetyl CoA inhibits the PDH reaction

PDH phosphatase is activated by Ca++, Mg++ and AMP; this will increase the rate of PDH reaction where as PDH kinase is inhibited by Ca++. When there is adequate ATP and acetyl CoA the enzyme is inhibited.