Diamino Acids

Diamino acids, acids containing two amino groups. In nature, d-arginine and d-lysine are found, which are part of the molecule of all proteins (only in some plant proteins is lysin absent). Proteins rich in residues of diamino acids (for example, histone, protamines) have an alkaline character. In the free state, diamino acids are found in germinating plant seeds, in very small quantities in some organs and tissues of animals, and in larger quantities in invertebrates. A product of artificial or biological breakdown of arginine is δ-ornithine (α, δ-diamino-valeric acid) NH₂.(CH₂)₃.CH(NH₂).COOH. When chickens are fed with benzoic acid, ornithuric acid (dibenzoyl derivative of ornithine) is excreted with urine. Free diamino acids found in the animal organism constitute only a small, unchanged part of the total amount of diamino acids formed as a result of biological breakdown of proteins, whereas the main part of diamino acids is converted into urea. In cystinuria, part of lysin, without passing into urea, may be excreted with urine. From diamino acids, by the removal of the CO₂ group, diamines can be formed (see): putrescine, cadaverine, and agmatine HN:C(NH₂).NH(CH₂)₄.NH₂, which is formed from arginine and found in ergot and in the hydrolysis products of herring milk. Diamino acids are very soluble in water, insoluble in alcohol and ether, have a sharply alkaline reaction, and are precipitated by phosphotungstic acid.