Tyrosine

TYROSINE, C₉H₁₁NO₃ (p-oxiphenyl-α-amino-propionic acid), HO.C₆H₄.CH₂.CH(NH₂).COOH

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An aromatic monoamino acid formed during the hydrolysis (acidic, alkaline, enzymatic) of proteins. In some animal proteins (silk fibroin and some other albuminoids^-) its content reaches 11-13%*, while in others (gelatin) it is absent, thereby determining their nutritional incompleteness. It is apparently not contained in completely fresh organs. T. has been found in certain varieties of aged cheese, in the contents of the small and large intestines, in the blood and urine of humans with acute yellow atrophy of the liver and in the final stages of phosphorus poisoning (also in liver tissue); it has been isolated from the urine of cystinurics, diabetics, and from various other types of pathological urine; it has been found in horse urine with peritoneal sarcomas; found in lobster meat, in ungerminated plant seeds, in lilac fruits, ficus leaves, Sccale cornutum, legume roots, in beet molasses. T., occurring in nature and obtained from the breakdown of proteins, is the L-isomer: [α]_D = -8.48° for 4-5% solutions in 21% HCl. Lippmann supposedly obtained d-T. from beet sprouts, Frankel from digested casein. The isolation of T. from protein hydrolysis products is based on its difficult solubility (1 part T. dissolves in 2,454 parts water at 20°, in 154 parts boiling water); upon neutralization of the hydrolysate, T. is isolated in the form of characteristic colorless, silky, fine needle-shaped crystals collected in bundles, odorless, with a slightly putrid taste; upon rapid heating, the crystals decompose with gas evolution at 310-314°. T. is insoluble in absolute alcohol, ether, easily soluble in alkalis and in diluted mineral acids, difficultly soluble in acetic acid; it is not precipitated by phosphotungstic acid, but is precipitated by mercuric nitrate, as well as by basic lead acetate from an ammoniacal solution. During putrefaction and under the action of pure cultures of some microorganisms (Bact. coli, Proteus, Subtilis, Bact. lactis aerog. etc.), T. undergoes various changes. Among the products formed during this process are: parahydroxycoumarinic acid, p-oxiphenylacetic acid, cresol, phenol, oxiphenyllactic acid, oxiphenylacrylic acid, benzoic acid, benzene, tyrosol, HO.C₆H₅.CH₂.CH₂.OH, tyramine, HO.C₆H₅.CH₂.CH₂.NH₂. The latter has been isolated from rotten meat, typhoid bacillus culture, from rotten fish liver, spleen autolysate, from peptic digestion products of ovalbumin, from may beetle extract, from casein hydrolysate, from Emmental cheese, ergot; Sammartino found tyramine in the thyroid gland. Tyramine is poisonous and causes contraction of smooth muscle. Tyrosol is formed from T. during alcoholic fermentation of sugar. Oidium lactis almost quantitatively converts T. into d-p-oxiphenyllactic acid, HO.C₆H₅.CH₂.CH(OH).COOH. In Gorgonia Cavelini and sponges, 3,5-diiodotyrosine has been found (see Skeletons). The thyroid hormone thyroxin is also a derivative of T. (see). The characteristic form of its crystals, as well as Millon's reaction (see), can serve for the detection of T. Mörner's test: green coloration upon boiling with a few cm³ of a mixture of 1 volume formalin, 45 volumes water, and 55 volumes concentrated H₂SO₄; phenols, homogentisic acid, proteins, and albumoses do not give Mörner's test. For colorimetric quantitative determination of T., the intense blue color that appears when a liquid containing T. is mixed with Folin and Denis reagent (a solution containing % sodium tungstate, 2% phosphomolybdic acid, and 10% phosphoric acid) and then alkalinized with soda is used. However, tryptophan and oxyproline also give blue coloration with this reagent and therefore must be previously removed. Tryptophan can be completely removed by precipitation with mercuric sulfate in 5% H₂SO₄.