Serine

SERINE (α-amino-β-hydroxypropionic acid, CH₂OH.CH.(NH₂).COOH). First isolated from silk glue by Cramer, later from a number of other proteins (serum albumin, milk albumin, fibrinogen, serum globulin, α-crystallin, β-crystallin, histone, nucleohistone, globin, salmine, whalebone, bovine horns, sheep horns, sheep wool, horse hair, glutin, silk fibroin, Canton sericin, Indian sericin, lens albumoid, Witte peptone, cow's milk casein). Serine is found in the brain and sweat. Only the left-handed (l-) isomer of serine is found in proteins; however, upon hydrolysis of proteins, optically inactive serine is obtained, as it racemizes during the processing. Racemic d,l-serine crystallizes in the form of thin leaflets; decomposition temperature is 245° (with the formation of gas); it is insoluble in alcohol and ether; it has a sweet taste. It easily forms compounds with copper oxide. The following compounds of d,l-serine are known: methyl and ethyl esters, monobenzoylserine, dibenzoylserine, naphthalene-sulfoserine, p-nitrobenzoyl-d,l-serine, d,l-phenyl-isocyanate of serine, d,l-α-naphthyl-isocyanate of serine; d,l-serine betaine. Yeast ferments d,l-serine partially, leaving d-serine; d-serine crystallizes in microscopically small needles or prisms; it is more soluble in water than the racemic form, decomposes with the formation of gas at 223°, and is sweeter than d,l-serine; d-serine possesses the same properties as l-serine, but is sweeter. The specific rotation of l-serine is [α]²⁰ = -6.87; in a 10% HCl solution [α]²⁰ = +14.32; d-serine gives the same values, but with the opposite sign. Serine was synthetically obtained by E. Fischer and Leuchs by the action of NH₃ and hydrocyanic acid on glycolaldehyde; for preparative purposes, chloroacetal can serve as the starting product. Upon reduction, serine converts into alanine; upon oxidation with nitric acid, it converts into glyceric acid. Fischer and Raske, by the action of barium hydrosulfide on α-amino-β-chloropropionic acid, obtained from serine ester, obtained cystine. Serine, by deaminating and passing through the stages of hydroxypyruvic acid and glycolaldehyde, apparently can be a source of glycogen formation in the organism. Upon decarboxylation, serine converts into aminoethyl alcohol, which participates in the construction of phosphatides (cephalins) and is also formed during putrefaction. Putrefactive bacteria, acting on serine, also yield propionic and formic acids.