Question

What is an effect of camp-dependent protein kinase (pka) inactivation of the liver isozyme but not the muscle isozyme?

Answer 1

The correct answer is "Glycolysis is inhibited in the liver but not muscle when blood sugar is low"

Step-by-step explanation:

Camp-dependent protein kinase (pka) is an enzyme that has multiple functions in the body, including regulation of glycogen and sugar metabolism. When blood sugar is low, the liver isozyme inhibits the action of pka, which causes an inhibitory effect of glucagon in glycolysis. However the muscle isozyme does not have an inhibitory effect on pka. Therefore, glycolysis is inhibited in the liver but not muscle when blood sugar is low.

Answer 2

The rate of glucogenesis and lipogenesis would drastically reduce. Protein kinase A acts to phosphorylate many enzymes important in metabolism. In the liver, protein kinase A phosphorylates acetyl-CoA carboxylase and pyruvate dehydrogenase. Such covalent modification has an inhibitory effect on these enzymes, thus inhibiting lipogenesis and promoting net gluconeogenesis. Insulin, on the other hand, decreases the level of phosphorylation of these enzymes, which instead promotes lipogenesis. Recall that gluconeogenesis does not occur in myocytes (muscle cells). Adrenaline and glucagon affect the activity of protein kinase A by changing the levels of cAMP in a cell via the G-protein mechanism, using adenylate cyclase.