Transamination of an amino acid transfers an amine group to form an α‑keto acid and is catalyzed by transaminases. Some amino acids can be transaminated into compounds that can be used directly in biological pathways, whereas other amino acids need to be converted through several steps. Match each amino acid to the appropriate category.

a. Yields a glycolytic or citric acid intermediate directly upon transamination

b. Requires several steps to yield a glycolytic or citric acid intermediate

Amino acids that fall under the first category are alanine, aspartate and glutamate. While amino acids that fall under the second category are glycine, valine, proline, leucine, isoleucine, methionine, serine, threonine, cysteine, asparagine, glutamine, phenylalanine, tryptophan, tyrosine, lysine, arginine and histidine

Explanation:

Alanine, a 3-carbon amino acid reacts with α-ketoglutarate, a 5-carbon ketoacid, to produce pyruvate, a 3-carbon compound which is one of the glycolytic products in aerobic respiration, and glutamate, a 5-carbon amino acid, with the aid of alanine transaminase (ALT). The amino group from alanine is transfered from the α-carbon of alanine to the α-carbon of the α-ketoglutarate.

Aspartate, a 4-carbon amino acid also reacts with α-ketoglutarate to form oxaloacetate, a 4-carbon ketoacid which is present as an intermediate in the citric acid cycle, and glutamate. The amino group transfer occurs between the α-carbon of aspartate and the α-carbon of α-ketoglutarate.

Unlike the presence of a ketoacid in the conversion of alanine and aspartate to their corresponding amino acids, glutamate conversion to α-ketoglutarate, an intermediate in the citric acid cycle, involves no ketoacids as an amino group acceptor from glutamate. The amino group is freely released as an ammonium ion. The reaction involves the presence of a cofactor, NAD + or NADP+, water (H2O) and glutamate dehygrogenase (GDH).

Other amino acids involve several metabolic steps to be converted into glycolytic or citric acid intermediates.