5o6 



ENZYMES 



colour is an oxidative process which takes place at P^ 6 ; this 

 red compound changes spontaneously by molecular rearrange- 

 ment, more rapidly on warming, into a colourless substance 

 without the intervention of tyrosinase ; finally, this colourless 

 substance is oxidized by oxygen to the black pigment melanin, 

 a change which is probably catalysed by a phenolase present 

 in the tyrosinase. 



The course of events is probably represented by the fol- 

 lowing formulas : — 



HO— 



/ 



-CH., . CH . NH, . COOH -» HO 



/ 



HO 



Tyrosine. 



CH, . CH . NH, . COOH 



3 : 4 dihydroxphenylalanine. 



o= 



/ 



O 



CH, . CH . NH , . COOH 



3 : 4 Quinone of phenylalanine. 



The dihydroxy phenylalanine is then further converted 

 through the 3 : 4 quinone of phenylalanine into the red 

 substance whose constitution is not yet definitely determined, 

 and this in turn gives rise to the colourless compound which 

 is probably an indole derivative, and it is this latter which 

 produces the black pigment melanin. 



CATALASE. 



This enzyme is widely distributed in aerobic plants and 

 animals ; it functions in the liberation of free molecular 

 oxygen from hydrogen peroxide and hence removes this toxic 

 substance from the cells. The action of catalase differs from 

 that of peroxidase which does not liberate molecular but 

 active atomic oxygen (see vol. ii.). 



FURTHER REFERENCES. 



Bayliss : " The Nature of Enzyme Action," London, 1919. 



Euler : " Chemie der Enzyme," Miinchen, 1922-1927. 



Griiss : " Biologie und Kapillaranalyse der Enzyme," Berlin, 1912. 



Oppenheimer : " Die Fermente u. ihre Wirkung," Leipzig, 1926. 



Effront : " Biochemical Catalysts in Life and Industry," New York, 



1917. 



Waksman and Davison : " Enzymes," London, 1926. 



