TYKOSINASE 79 



is so intimately bound with the cell that it cannot be obtained 

 in extracts until after the cells are dead, but is present in ex- 

 pressed cell-juices. It can be isolated by the usual methods, is 

 destroyed by boiling, and its action is inhibited by CNH. It 

 has been demonstrated in nearly all organs and tissues except 

 pancreas, muscle, marrow, and mammary gland ; it is present 

 in the blood in small amounts, but not at all in the bile (Jaco- 

 by 1 ). It is most abundant in the liver and spleen, and is 

 present in pig embryos, 9 cm. long, but not in those 2-3 cm. 

 long. Jacoby has obtained a body with the properties of alde- 

 hydase which did not give proteid reactions. It is a true 

 enzyme, since it oxidizes aldehydes 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 substance, laccol, which is a member of 

 the aromatic series. He later found in a number of plants an 

 enzyme acting on ty rosin, distinct from the laccase, which he 

 named tyrosinase. Biederman 2 later found tyrosinase in the 

 intestinal fluid of meal worms, v. Fiirth and Schneider 3 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 spe- 

 cific for tyrosin, frequently oxidizing other substances, v. Fiirth 

 and Schneider found the product of oxidation of tyrosin by 

 animal tyrosinase related to certain of the melanins of animal 

 tissues, and believe that tyrosinase is responsible for the pro- 

 duction 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. 

 Florence Durham 4 suggests that tyrosinase in the skins of ani- 

 mals is responsible for their pigmentation. 



Gonnermann 5 found that tyrosinase from beet-root produced 

 homogentisic add by acting on tyrosin, which is of interest in 

 connection with the congenital hereditary disease, alkaptonuria 



1 Ergebnisse der PhysioL, 1902 (Bd. I, Abt. 1), p. 213, where is also given 

 a resume of the subject of intracellular enzymes. 

 'Pfliiger's Arch., 1898 (72), 105. 

 3 Hofmeister's Beitr., 1901 (1), 229, 



4 Proc. Eoyal Soc., 1904 (74), 310. 



5 Pfliiger's Arch., 1900 (82), 289. 



