Practical physiological chemistry; a book designed for use in courses in practical physiological chemistry in schools of medicine and of science . no acid. However, about 11 per ^ Kurajeff: Zeit. physiol. Client., 36, 501, 1898-99. * Osborne and Mendel: Joitr. Biol. Chem., 20, 357, 1915. 78 PHYSIOLOGICAL CHEMISTRY cent was obtained by Abderhalden from globin, the protein constituentof oxyhemoglobin, and about 13 per cent by Kossel and Kutscher fromthe protamine stiirine. Crystals of histidine dichloride are shown in Fig. 27. Knoops Color Reaction for Histidine.—To an aqueous solution of histid
Practical physiological chemistry; a book designed for use in courses in practical physiological chemistry in schools of medicine and of science . no acid. However, about 11 per ^ Kurajeff: Zeit. physiol. Client., 36, 501, 1898-99. * Osborne and Mendel: Joitr. Biol. Chem., 20, 357, 1915. 78 PHYSIOLOGICAL CHEMISTRY cent was obtained by Abderhalden from globin, the protein constituentof oxyhemoglobin, and about 13 per cent by Kossel and Kutscher fromthe protamine stiirine. Crystals of histidine dichloride are shown in Fig. 27. Knoops Color Reaction for Histidine.—To an aqueous solution of histidineor a histidine salt in a test-tube add a little bromine water. A yellow colorationdevelops in the cold and upon further addition of bromine water becomes perma-nent. If the tube be heated/ the color will disappear and will shortly be re-placed by a faint red coloration which gradually passes into a deep wine black, amorphous particles separate out and the solution becomesturbid. The reaction cannot be obtained in solutions containing free is best to use such an amount of bromine as will produce a permanent ?V C^. Fig. 27.—Histidine Dichloride. yellow color in the cold. The use of a less amount of bromine than thisproduces a weak coloration, whereas an excess of bromine prevents thereaction. The test is not very delicate, but a characteristic reactionmay always be obtained in i : 1000 solutions. The only histidine de-rivative which yields a similar coloration is imidazolethylamine, andthe reaction in this case is rather weak as compared with the color ob-tained with histidine or histidine salts. Valine, C5H11NO2.—The amino-valerianic acid obtained fromproteins is a-amino-isovalerianic acid, and as such bears the followingformula: CH3 NH2 H—C C—COOH. CH3 H ^ The same reaction will take place in the cold more slowly. PROTEINS 79 It closely resembles leucine in many of its properties, but is more solublein water. It is a difficult matter to identi
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