158 THE PROTEIN SUBSTANCES. 



which turns deep -wine-red, later becoming cloudy, due to the forma- 

 tion of dark amorphous particles (F. KNOOP 1 ). 



It gives a very beautiful diazo-reaction with diazobenzenesulphonic 

 acid in solutions made alkaline with sodium carbonate, which according 

 to PAULYIS deep cherry-red in dilutions of 1:20,000 and still markedly 

 red in 1 : 100,000 (tyrosine gives a similar reaction) . 



Histidine is sometimes classified in a group, with the two diamino- 

 acids, arginine and lysine which KOSSEL has called the hexone bases. 



Arginine (guanidine-a-aminovaleric acid), 



( HN > C <NH 2 CH 2 



C 6 Hi 4 N 4 2 = (CH 2 ) 2 , 



CH(NH 2 ) 

 COOH 



first discovered by SCHULZE and STEIGER in etiolated lupin- and pumpkin- 

 sprouts, has later been found in other germinating plants, in tubers and 

 roots. GULEWITSCH has found arginine in the ox-spleen. It was first 

 found by HEDIN as a cleavage product of horn substance, gelatin, and 

 several proteins, and then by KOSSEL and his pupils as a general cleav- 

 age product of protein substances as a class. The greatest quantity was 

 obtained from the protamines; but the histones and certain plant pro- 

 teins, edestin and the protein from pine seeds and especially excelsin 

 (14.14 per cent), also yield abundant arginine. Arginine also occurs 

 among the products of tryptic digestion (KOSSEL and KUTSCHER 2 ) . 



On boiling with baryta-water, as well as by the action of an enzyme, 

 arginase, discovered by KOSSEL and DAKIN, S arginine yields urea and 

 ornithine. Arginine has been prepared synthetically from ornithine 

 (a-^-diamino-valeric acid) and cyanamide by SCHULZE and WINTER- 



STEIN. 4 



Arginine crystallizes in rosette-like tufts, plates, or thin prisms, is readily 

 soluble in water with alkaline reaction and nearly insoluble in alcohol. 

 With several acids and metallic salts it forms crystalline salts and double 

 salts respectively. Its acidified watery solution is precipitated by 

 phosphotungstic acid. The most important salts are the copper-nitrate 

 (C6H 14 N 4 O 2 )2.Cu(NO3) 2 +3H 2 O and the silver salts C 6 Hi 4 N 4 O 2 .HNO 3 + 



1 Hofmeister's Beitrage, 11. 



2 Schulze and Steiger, Zeitschr. f. physiol. Chem., 11; Schulze and Castoro, ibid., 41; 

 Gulewitsch, ibid., 30; Hedin, ibid., 20 and 21; Kossel and Kutscher, -ibid., 22, 25, 26. 



3 Zeitschr. f. physiol. Chem., 41, and Dakin, Journ. of biol. Chem., 3. 



4 Ber. d. d. chem. Gesellsch., 32 and Zeitschr. f. physiol. Chem., 34. 



