Question

1. (b) Using three examples, outline how amino acids can act as precursors of other important nitrogen-containing compounds in the body

biochem

Answer 1

amino acids can be categorised in two types essential (which we take from outside) & non-essential (which build inside body) amino acids. many amino acids serve as precusor of other important compounds in the body. some examples are given below -:

Histamine, a potent vasodilator, is derived from histidine by decarboxylation. Tyrosine is a precursor of the hormones thyroxine (tetraiodothyronine) and epinephrine and of melanin, a complex polymeric pigment. The neurotransmitter serotonin (5-hydroxytryptamine) and the nicotinamide ring of NAD⁺ are synthesized from tryptophan. Glutamate is a precursor of ?-aminobutyrate (GABA). Aspartate is a precursor of ?-alanine.

Nitric Oxide, a short-lived signal molecule, is formed from Arginine

Nitric oxide (NO) is an important messenger in many vertebrate signal-transduction processes. This free-radical gas is produced endogenously from arginine in a complex reaction that is catalyzed by nitric oxide synthase. NADPH and O₂ are required for the synthesis of nitric oxide. Nitric oxide acts by binding to and activating soluble guanylate cyclase, an important enzyme in signal transduction.

HO NH2 NH 2 H20 NADPH NADP 2 H20 NADPH NADP +NO Hs +H Arginine N-w-Hydroxy- arginine Citrulline Nitric oxide

Glutathione, a Gamma-Glutamyl Peptide, Serves as a Sulfhydryl Buffer and an Antioxidant, derived from glutamate, cysteine & glycine

Glutathione, a tripeptide containing a sulfhydryl group, is a highly distinctive amino acid derivative with several important roles. For example, glutathione, present at high levels (?5 mM) in animal cells, protects red cells from oxidative damage by serving as a sulfhydryl buffer. It cycles between a reduced thiol form (GSH) and an oxidized form (GSSG) in which two tripeptides are linked by a disulfide bond. GSSG is reduced to GSH by glutathione reductase, a flavoprotein that uses NADPH as the electron source. The ratio of GSH to GSSG in most cells is greater than 500. Glutathione plays a key role in detoxification by reacting with hydrogen peroxide and organic peroxides, the harmful by-products of aerobic life.

2 GSH + RO-OH ß--------à GSSG +H₂O + ROH

SH OOC COO H NH y-Glutamate Cysteine Glycine

Glutathione tripeptide consists of a cysteine residue flanked by a glycine residue and a glutamate residue that is linked to cysteine by an isopeptide bond between glutamate's side-chain carboxylate group and cysteine's amino group.