Does ADP allosterically activate or inhibit pyruvate kinase in Glycolysis? Or does it play a role in the allosteric regulation? If so, how?

Question

I cannot find anywhere in my textbooks or scientific literature if whether or not ADP plays a role in allosterically activating or inhibiting pyruvate kinase in the glycolytic pathway. I know that ATP inhibits pyruvate kinase but I need to know the regulatory effect of ADP on pyruvate kinase. Thank you.

Answer 1

So as you may know there are three main regulations of the glycolytic pathway: phosphofructokinase, hexokinase, and pyruvate kinase with the first two regulation steps occurring in the cytoplasm and the last regulation step occurring in the mitochondria.

In the terms of your question we must look into the reaction step of pyruvate kinase and the factors that up regulate and down regulate its function enzymatically. In the reaction scheme (last step of glycolysis occurring in the mitochondria), PEP or phosphoenolpyruvate undergoes a phosphoryl transfer (delta G is -31.4 kj/mol) to undergo the production of pyruvate.Since this reaction is a phosporyl transfer, we obtain our second ATP formation of ADP to ATP (ADP accepts the P group); remember the first ATP formed occurs in the reaction involving phosphoglycerate kinase.

It should be remembered that all kinases need a metal cation as a cofactor such as Mg 2+.

Now lookin in terms of regulation; one of the regulation factors is ATP which gets really high with the needs of the cell energy change which will result in ATP allosteric inhibition of our enzyme. Another factor is the amino acid alanine in which this acts as a allosteric inhibitor because its concentration being abundant means that the cell contains enough building blocks around in the environment. (this is occurring in muscle cell)

Looking at the same enzyme in terms of the liver cell, our enzyme is actually controlled by a reversible phosphorylation. Decreased blood levels causes glucagon-triggered cAMP cascade that leads to the phosphorylation of pyruvate kinase to stop activity. This prevents liver consumption of glucose so that the brain and muscle cells have access to glucose first.