Tryptophan

TRYPTOPHAN (former name protein-chromogen), C₁₁H₁₂N₂O₂, indole-α-aminopropionic acid, an amino acid obtained in the hydrolysis of proteins by the action of trypsin, bacteria, barium water; in acid hydrolysis, the greater part of T. is destroyed. T. is found in the free state in the spleen of ox, horse, in cheese, in fish meat, in germinating seeds, in the juice of germinating beet stems, and is formed in the hydrolysis of bee venom with hydrochloric acid. T. is a component of many proteins (albumins and globulins of animal and vegetable origin, casein, vitellin, globin, etc.). Some albuminoids, protamines (salmine), as well as gliadin, zein do not contain T. T. was artificially synthesized by Ellinger and Flamand from β-indole aldehyde. Natural T. is levorotatory; it racemizes upon 12-hour heating with 25% hydrochloric acid at 170°, and according to some authors even upon recrystallization from hot pyridine. The specific rotation of T. has not been precisely determined, which apparently depends on its easy racemization; for example, for aqueous 0.5% solution of T. [α]_D = from -29.75 to -40.3; 10-11% solutions in NaOH give [α]_D^20° = from +6.06 to +6.57. T. crystallizes in the form of silky rhomboidal and hexagonal plates. Racemic T. has a slightly sweet taste, the active form is tasteless. T. is difficultly soluble in cold water, well in hot water, poorly in cold pyridine, well in hot pyridine; in absolute alcohol it dissolves poorly even upon heating. Data regarding the melting point are contradictory, apparently depending on the rate of heating. According to Abderhalden and Kempe, upon rapid heating T. melts at 289°, according to Hopkins and Cole, at 252°. T. gives a series of compounds, some of which can be used for its isolation: for example, sodium salt of 1-β-naphthalenesulfotryptophan, crystals melting at 304°, l- and d-1-benzenesulfotryptophan, compounds with picric acid, with formaldehyde and other aldehydes; copper salt of T. does not crystallize, is difficultly soluble in ordinary solvents. Many compounds of T. are colored: it is assumed that melanoidin substances are formed at the expense of T. For the detection of free T. the following reaction is used: a solution of T., acidified with acetic acid, upon addition of Br- or Cl-water is colored pink, which turns yellow with excess of Br or Cl; then the Romieu reaction, which can be used by histologists: upon addition of syrupy phosphoric acid and subsequent weak heating, proteins are colored pink-red; Liebermann reaction, Adamkiewicz reaction (see) and others.--In the animal organism T. is not synthesized; therefore its presence in food is necessary; proteins that do not contain T. are not complete. Absence of T. in food leads to loss of weight, blindness (Curtis); apparently tryptophan also serves as material for the formation of blood, urinary (urochrome) and other pigments. In the intestine under the action of aerobic putrefactive bacteria from T. indole and skatole are formed, which are absorbed into the blood and pass to the liver where they give ethylsulfuric acids. Yeasts in the presence of sugar convert T. into tryptophol (indole ethyl alcohol), Oidium lactis into indole lactic acid; Bact. subtilis gives anthranilic acid (o-aminobenzoic acid); anaerobic bacteria give indole propionic acid. In the organism of dog and coyote T. is converted into kynurenic acid (see), which is excreted with urine; the intermediate product of this transformation is apparently kynurenine with the formula C₁₀H₁₀N₂O₂ = CH.CH(NH₂).COOH, which is also connected with the formation of urochrome. For the quantitative determination of T. in proteins the colorimetric method of Furth can be used, based on the Voisenet reaction: upon addition to a tryptophan solution of formaldehyde (benzaldehyde), concentrated HCl and NaNO₂, a violet (blue) coloration is obtained. Error up to 10%. Necessary solutions: 1) 2% solution of NaF, in 1 cm³ of which there is 1 mg T. (can stand for a long time); 2) 0.05% solution of NaNO₂ (prepared before use from 5%); 3) 2.5% solution of formaldehyde or 1.9% benzaldehyde in concentrated HCl; 4) concentrated HCl. The protein is hydrolyzed with trypsin or 20-30% solution of NaOH. After neutralization of the hydrolysate, 2 cm³ of the solution (its volume is calculated so that the concentration of T. is from 0.05% to 0.20%) are taken in a 20 cm³ measuring flask and 1 drop of formaldehyde (benzaldehyde) and 15 cm³ of HCl are added; the liquid turns yellow; after 10 minutes 10 drops of NaNO₂ solution are added and made up to the mark with concentrated hydrochloric acid. The amount of NaNO₂ should correspond to the content of T. If a precipitate falls upon addition of HCl, it is filtered. In the same way a standard is prepared from solution (1). Nery recommends taking instead of formaldehyde a 2% solution of dimethylamidobenzaldehyde in amyl alcohol (2 drops); add NaNO₂ solution until the color stops intensifying; colorimetry after 30 minutes. Oxytryptophan found by Abderhalden and Kempe, as well as by other authors, is apparently a product formed from T. under the influence of processing.