oxii)i7A\<; j:\zy ]n:s 73 



abundant in the liver'''' and si)l(M'n, and is )»rcsriii in |)i<f (■inl)ryos, 

 9 cm. lony, but not in those 2-:} em. Ionj>'. .Jacoby luis ol)tained a body 

 with the properties of aldehydase which diil not <^ive protein re- 

 actions. It is a true enzyme, since it oxidizes aldeliydes without itself 

 being used up. Its range of action is limited, for Jacoby found it 

 without effect upon acetic acid and stearic acid. 



Tyrosinase. — This enzyme, which is found both in animal and plant 

 tissues, is particularly interesting in relation to the formation of 

 pigments. Bertrand found that the transformation of the juice of 

 lac-yielding plants into the black lacquer was brought about by the 

 action of an oxidizing ferment, laccase, upon an easily oxidized sub- 

 stance, laccol, which is a member of the aromatic series. He later 

 found, in a number of plants an enzyme acting on tyrosine, distinct 

 from the laccase, which he named tyrosinase. Biederman later found 

 tyrosinase in the intestinal fluid of meal worms, v. Fiirth and 

 Schneider found a similar enzyme in the hemolymph of insects and 

 arthropods, which explains its darkening when exposed to air. This 

 enzyme, as obtained from different sources, is not always specific for 

 tyrosine, frequently oxidizing other substances. As yet the chemical 

 processes and end results of the oxidation of tyrosine by tyrosinase 

 are unknown. Bach ^"^'^ obtained evidence that tyrosinase is not a 

 specific oxidizing enzyme, but consists of an aminoacidase, which dis- 

 integrates the tyrosine and makes it susceptible to the action of pheno- 

 lase which is the oxidizing agent, v. Fiirth and Schneider found the 

 product of oxidation of tyrosine by animal tyrosinase related to cer- 

 tain of the melanins of animal tissues, and believe that tyrosinase is 

 responsible for the production of many normal pigments. In the 

 ink-sacs of the squid, which eject an inky fluid containing melanin- 

 like pig-ment, tyrosinase was also found, corroborating this hypothesis, 

 and it is probable that tyrosinase in the skins of aninmls is responsible 

 for their pigmentation.*" Bacteria also contain tyrosinase,"" and this 

 or similar enzymes seem to be present in melano-sarcomas."^ 



Gonnermann "- found that tyrosinase from beet-root produced 

 homogentisic acid by acting on tyrosine, which is of interest in con- 

 nection with the congenital hereditary disease, alkaptonuria {q. v.)y 

 in which the urine becomes dark upon exposure because of the pres- 

 ence of homogentisic acid. The action of tyrosinase upon the aromatic 

 radicals of proteins is of great importance in the study of both 

 physiological and pathological pigment formation, and hence has re- 



ssBattelli and Stern. Biocliem. Zeit., 1910 (29), 130. 

 ssaBiochem. Zeit., 1914 (60). 221. 



89 Meirovvsky, Cent. f. Path., 1909 (20), 301. 



90 Lehmann "and Sano, Arch. f. Hyg., 1908 (67), 99. 



91 Alsberg, Jour. Med. Res., 1907' (16). 117: Neuberfj:, Virchow's Arcliiv., 190S 

 (192), 514; Gessard, Compt. Rend. Soc. Biol., 1902 (54), 1305. 



92 Pfluger's Arch., 1900 (82), 289. 



