Regulation of Pyruvate Dehydrogenase Flashcards
(20 cards)
True or false: The conversion of pyruvate to acetyl CoA by pyruvate dehydrogenase is reversible.
False; it is irreversible.
Which compounds are competitive inhibitors of pyruvate dehydrogenase?
NADH and acetyl-CoA (the products of the reaction)
True or false: NAD+ is a competitive inhibitor of pyruvate dehydrogenase.
False; NADH is a competitive inhibitor (competes for NAD+ binding site)
True or false: Acetyl-CoA is a competitive inhibitor of pyruvate dehydrogenase.
True
What two molecules actually drive the E2 and E3 reactions of pyruvate dehydrogenase in reverse?
NADH and acetyl-CoA
What is the effect of high ratios of [NADH]/[NAD+] and [acetyl-CoA]/[CoA]?
Maintains E2 in acetylated form, making it incapable of accepting hydroxyethyl group from TTP
Which part of pyruvate dehydrogenase reaction is inhibited by NADH?
The dihydrolipoyl dehydrogenase (E3).
Which part of pyruvate dehydrogenase reaction is inhibited by acetyl-CoA?
The transacetylase component (E2), because acetyl-CoA binds to it.
To what fate does the oxidative carboxylation of pyruvate to acetyl-CoA commit the carbon atoms derived from glucose?
Either oxidation to CO2 by the TCA cycle and generation of energy or incorporation into lipid (because acetyl-CoA is a precursor for lipid synthesis).
What are the two key means of regulating pyruvate dehydrogenase?
1) Competitive inhibition by NADH and acetyl CoA
2) Covalent modification of E1 by pyruvate dehydrogenase kinase that inactivates the enzyme.
Which hormone reverses the inactivation of pyruvate dehydrogenase kinase by activating pyruvate dehydrogenase phosphatase?
Insulin
What activates pyruvate dehydrogenase kinase?
NADH and acetyl-CoA
When activated, what does pyruvate dehydrogenase kinase do to pyruvate dehydrogenase?
It causes phosphorylation that inactivates the multi-enzyme complex.
Which enzyme, when activated by insulin, reverses the effects of pyruvate dehydrogenase kinase? How does it do this?
Pyruvate dehydrogenase phosphatase; it removes phosphoryl groups, reactivating pyruvate dehydrogenase and allowing the TCA Cycle to continue.
What causes insulin to promote the synthesis of acetyl-CoA and glycogen?
Increased [glucose].
True or false: the phosphorylated E1 enzyme is active.
False; the dephosphorylated E1 enzyme is active.
What causes the deactivation of the E1 enzyme?
Phosphorylation by pyruvate dehydrogenase kinase, which is activated by increase concentrations of NADH and Acetyl-CoA
What inhibits pyruvate dehydrogenase kinase?
Pyruvate, ADP, and Ca+
True or false: pyruvate dehydrogenase is activated by cAMP.
False; it is unaffected by cAMP.
True or false: Ca2+ (released in response to hormones) activates pyruvate dehydrogenase kinase and inhibits pyruvate dehydrogenase phosphatase.
False; Ca2+ inhibits pyruvate dehydrogenase kinase and activates pyruvate dehydrogenase phosphatase.
