Urea is the end product of protein metabolism. The nitrogen of amino acids converted to ammonia is toxic to the body. It is converted to urea and detoxified. As such, urea accounts for 80%–90% of the nitrogen-containing substances excreted in urine.

Amino acids are converted to the respective amines by decarboxylation process. This is carried out by a group of enzymes called decarboxylase. The coenzyme involved in the reaction is PLP (pyridoxal phosphate). Biogenic amines, which have important functions, are synthesised by PLP decarboxylation. Serotonin – Neurotransmitter regulates sleep, behaviour, and blood pressure. Histamine – Vasodilator lowers BP,…

The sulphur amino acids, namely cysteine and homocysteine, undergo deamination coupled with desulphydration to give keto acids.

Serine, threonine, and homoserine are the hydroxyl amino acids; they undergo nonoxidative deamination catalysed by PLP-dependent hydrases.

Amino acid which is deaminated to liberate without undergoing oxidation is termed as non-oxidative deamination.

D-amino acids are present in the plants and cell walls of microorganisms and are not used in the biosynthesis of mammalian proteins. They are present in the diet and are metabolised by liver. D-amino acid is an FAD-dependent enzyme that catalyses the oxidative deamination of these unnatural isomers of amino acids. The resulting α-keto acid…

α-amino acid oxidase and D-amino acid oxidase are flavour proteins, processing FMN and FAD, respectively. They act on amino acids (L and D) to produce α-keto acids and NH3. In this reaction, O2 is reduced to H2O2, which is later decomposed by catalase.

Glutamate dehydrogenase is zinc, containing mitochondrial enzyme. GDH is controlled by allosteric regulation. ATP and GTP inhibit GDH, whereas ATP and GTP activate GDH. Protein-rich diet: Glutamate level is elevated, which is converted to α-ketoglutarate with liberation of NH3. When the energy levels are low, the dehydration of glutamate is increased to provide α-ketoglutarate, which…

Conversion of glutamate to α-ketoglutarate occurs through the formation of an intermediate α-imminoglutarate.

In the process of transamination, the amino groups of most amino acid are transferred to α-ketoglutarate to produce glutamate. The glutamate serves as a collection centre for amino groups in the biological system. Glutamate rapidly undergoes oxidative deamination catalysed by glutamate dehydrogenase (GDH) to liberate ammonia. This enzyme is unique, in that it can utilise either NAD+ or…