Mix thoroughly and then introduce an equal volume of concentrated sulphuric acid by means of a pipette reaching to the bottom of the test tube so as not to mix the acid and the solution. To a little protein solution add an equal volume of a solution of glyoxylic acid made by reducing oxalic acid with sodium amalgam. Glyoxylic Acid Reaction.-This reaction is produced with proteins by the action of glyoxylic acid, CH(OH)2- COOH (p. The test detects the indole ring structure of the tryptophane residue. īrustier and coworkers utilized the Adamkiewicz-Hopkins-Cole reaction as an identity test for gramicidin121. Īpproximately this quantity of mercuric sulfate is necessary to precipitate the tryptophane completely, as judged by the Hopkins-Cole glyoxylic acid test.
Almost all so-called alka-loidal reagents will precipitate proteins in slightly acid solution. a blue color when boiled with ninhydrin ( triketohydrindene hydrate), which is intensified by the presence of pyridine (c) Millon s test for tyrosine, a brick-F color or precipitate when boiled with mercuric nitrate in an excess of nitric acid (d) Hopkins-Cole test for tryptophan, a violet zone with a salt of glyoxylic acid and stratified over sulfuric acid and (e) xanthoproteic test, a brilliant orange zone when a solution in concentrated nitric acid is stratified under ammonia. Proteins respond to the following color tests (a) biuret, pink to purple with an excess of alkali and a small amount of copper sulfate (b) ninhydrin.
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