Leucine

LEUCINE, C₆H₁₃NO₂, one of the amino acids, occurs in nature in the form of 3 isomers. 1) l-leucine, α-aminoisobutyric acid: ^3N)CH-CH₂-CH(NH₂)-COOH. It crystallizes in brilliant, white, very thin plates, rather difficultly soluble in water. The taste is bitter. It is a product of the hydrolysis of most animal and vegetable proteins. It is contained in small amounts in blood, milk, often in pus, atheromas, and scales in ichthyosis. Found in significant amounts in urine in acute yellow atrophy of the liver (sometimes even as a precipitate), in poisoning by phosphorus and arsenic due to the sharp increase in protein breakdown and decrease in the urea-forming function of the liver; it also appears in urine in cystinuria. Under the influence of yeast, it turns into isoamyl alcohol (see Fermentation). 2) d-isoleucine, α-amino-β-methylpropionic acid, C₅H₁₁CH-CH(NH₂)-COOH; C₂H₅ is found together with l-leucine; crystallizes in plates or rods and rhombic tablets. More soluble in water than the previous one. The taste is bitter, harsh. 3) d-norleucine, δ-aminocaproic acid, CH₃-CH₂-CH₂-CH₂-CH(NH₂)-COOH. Isolated from nerve tissue proteins. Crystallizes in six-sided plates joined in druses. The taste is slightly sweet. Difficultly soluble in water.