AP BIOLOGY

Detailed explanation-1: -Pyruvate carboxylase is a multisubunit enzyme that has acetyl CoA as a positive allosteric regulator. The enzyme is critical for both gluconeogenesis and fatty acid synthesis, since it replenishes the citric acid cycle intermediates (malate or citrate) that leave the mitochondria as part of biosynthetic processes.

Detailed explanation-2: -The activity of the biotin-dependent enzyme pyruvate carboxylase from many organisms is highly regulated by the allosteric activator acetyl-CoA. A number of X-ray crystallographic structures of the native pyruvate carboxylase tetramer are now available for the enzyme from Rhizobium etli and Staphylococcus aureus.

Detailed explanation-3: -Citrate, an allosteric activator of acetyl-CoA carboxylase, induces polymerization of an inactive protomeric form of the enzyme into an active filamentous form composed of 10-20 protomers.

Detailed explanation-4: -Acetyl CoA carboxylase, the rate-limiting enzyme in regulating fatty acid synthesis, is thought to be controlled by allosteric effectors, its state of aggregation, covalent modulation and protein inhibitors.

Detailed explanation-5: -Since the acetyl-coA carboxylase reaction is the committed step in fatty acid synthesis, its regulation has been actively investigated in many laboratories. It has long been known that citrate is an allosteric activator of the enzyme.