The co-factor PLP is utilized frequently in amino acid metabolism. Remarkably, P

Question

The co-factor PLP is utilized frequently in amino acid metabolism. Remarkably, PLP is involved in the cleavage of different bonds with the alpha-Cof amino acids, depending on the different enzymes in which it functions. First, give examples of different bonds that are broken in two different amino acids (include the name of the enzyme in which PLP functions). Next, explain how different bonds with alpha-C can be broken using the common co-factor, PLP.

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Explanation / Answer

The mechanisms involving a Schiff base linkage of the amino group to PLP. The prosthetic group of the transaminase enzyme is pyridoxal phosphate (PLP), a derivative of vitamin B6.

Amino Acids that are Catabolized into Pyruvate. Alanine transaminase reversibly transfers the amino group from alanine to ?-ketoglutarate to form pyruvate and glutamate. Note that enzyme requires a pyridoxal phosphate cofactor. The ?-ketoglutarate is regenerated by glutamate dehydrogenase.

Serine dehyratase is another enzyme that requires a pyridoxal phosphate cofactor. This enzyme catalyzes the ?-elimination of the hydroxyl group of serine to form an amino acrylate intermediate which tautomerizes into the imine which is then hydrolyzed to produce ammonia and pyruvate.

Glycine is converted into pyruvate via conversion of glycine to serine by serine hydroxymethyl transferase which is an incredibly interesting enzyme. It contains a pyridoxal phosphate cofactor and a N5 ,N10-methylene-tetrahydrofolate which is a cofactor we have not encountered yet. The N5 ,N10- methylene-tetrahydrofolate is produced by the glycine cleavage system which transfers a methylene group from glycine to THF. The THF cofactor is a one carbon acceptor and donor.

Aspartate and asparagines are both degraded into oxaloacetate. Aspartate is converted into oxaloacetate by aspartate amino transferase which is a PLP enzyme that transfers an amino group from aspartate to ??ketoglutarate to form glutamate and oxaloacetate.

Cystathionine ?-synthase is a PLP dependent enzyme that catalyzes the condensation of a serine residue with homocysteine to form cystathionine.

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