Question

1-What are the major TCA cycle regulation sites, and what are the effectors?

2-List the five coenzymes required by the enzymes of the PDHC . Do they function as prosthetic groups or as cosubstrates?

Answer 1

1. Regulation of citric acid cycle:
The TCA cycle is regulated by the metabolic/energy needs of the cell

i. Citrate synthase inhibitors = ATP, NADH, and succinyl CoA.

ii. Isocitrate dehydrogenase activator = ADP
Inhibitors = ATP and NADH

iii. Alpha-Ketoglutarate dehydrogenase inhibitors = Succinyl CoA and NADH

iv. Fluoroacetate is a suicide substrate of aconitase.

2. Pyruvate dehydrogenase catalyzes the oxidative decarboxylation of pyruvate to produce Acetyl CoA. It requires five cofactors
i. NAD+
ii. FAD
iii. Coenzyme A
iv. Lipoid acid
v. Thiamine pyrophosphate
It also requires Mg+2 for its activity.
Many of these cofactors also serve as cosubstrates.

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