OXIDIZING ENZYMES 67 



used up. Its rariRo of actiou is limited, for Jacoby found it mthout effect upon 

 acetic acid and stearic acid. 



Tyrosinase. — Tliis cnzyine, which is found both in animal and plant tissues, 

 is particularly iiitcrostinu; in relation to the formation of pigments. Bcrtrand 

 found tliat the traiisforiuatiou of the juice of lac-yicldin^!; plants into the black 

 lacquer was liroufiht al)()ul by the action of an oxi<lizinK ferment, Ificrane, upon an 

 easily oxidized sulistance, laccnl, which is a menil)er of the aromatic series. He 

 later found in a numl)er of j)lants an enzyme acting on tyrosine, distinct from the 

 laccase, whicii he named tyrosinase, liiedcrman 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 disintegrates the tyrosine and makes it sus- 

 ceptible to the action of phenolase which is the oxidizing agent, v. Fiirth and 

 Schneider found the product of oxidation of tyrosine by animal tyrosinase related 

 to certain of the melanins of animal tissues, and believe that tyrosinase is respon- 

 sible for the production of many normal pigments.-** In the ink-sacs of the squid, 

 which eject an inky fluid containing melanin-like pigment, tyrosinase was also 

 found, corroborating tliis hypothesis, and it is probable that tyrosinase in the skins 

 of animals is responsible for their pigmentation. -^ Bacteria also contain tyrosi- 

 nase,'" 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, wliich is of interest in connection with the congenital 

 hereditary disease, alkaptonuria (q. v.), in which the urine becomes dark upon 

 exposure because of the presence 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 received ex- 

 tensive study, which ^^•ill be found fully described in the monograph by Kastle 

 (loc. cit.)^' and under the appropriate subjects in subsequent chapters. 



Other Oxidizing Enzymes. — Of the great number of other less studied oxidizing 

 enzymes little can be definitely stated. Some consider that they are largely dif- 

 ferent manifestations of the action of one oxidizing ferment, but against this view 

 Jacoby mentions that they occur distributed imequally in different organs, can be 

 separated from each other, and they cause different reactions. For the catalase 

 and for laccase (which produces the Japanese lacquer by an oxidizing process) 

 and perhaps for other oxidizing ferments, iron and manganese may be essential 

 constituents. Of particular significance for pathology are the enzymes which 

 accomplish the oxidation of purines to uric acid and the subsequent destruction of 

 uric acid. These are discussed in Chapter xxiii. Also the enzymatic oxidation 

 and reduction of /3-oxybutyric acid and aceto-acetic acid in the liver, as studied by 

 Dakin and Wakeman,'-^ are of great importance in acidosis {q. v.). 



Reducing enzymes have not yet been satisfactorily demonstrated.^^ It is 

 possible that they do not exist, and that the intracellular reductions that are 

 carried on within the cells are brought about by simple chemical reactions inde- 

 pendent of catalysis. The best known intracellular reduction is that of methylene 

 blue, ^5 which can be readily studied experimentally because the blue color dis- 



"Biochem. Zeit., 1914 (60), 221. 



=8 Bloch (Zeit. physiol. Chem., 1917 (100), 226) describes under the name 

 dopaoxidase an enzj-me present in the protoplasm of the basal epidermal and hair 

 follicle cells, which acts specifically on 3, 4 — dihydroxyphenylalanine, causing 

 oxidation and condensation with formation of a dark brown or black pigment. 



29 Meirowsky, Cent. f. Path., 1909 (20), 301. 



30 Lehmann and Sano, Arch. f. Hyg., 1908 (67\ 99. 



31 Alsberg, Joiu-. Med. Res., 1907 (16), 117; Neuberg, Virchow^'s Archiv., 1908 

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



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



"Jour. Amer. Med. Assoc, 1910 (54), 1441. 



" See Heffter, Arch. exp. Path. u. Pharm., 1908, Suppl., p. 253. 



36 See Thunberg, Skand. Arch. Physiol., 1917 (35), 163. 



