84 



vestigations indicate: first, that mela- 

 nin is produced by the oxidation of 

 certain products of protein metabolism 

 by the action of specific enzymes; sec- 

 ond, that this reaction takes place in 

 the cytoplasm of cells probably by 

 enzymes secreted by the nucleus; 

 third, that various chromogens are 

 used, the particular ones oxidized de- 

 pending on the character of the en- 

 zymes present; and finally that hered- 

 itary differences in color are due to 

 hereditary differences in the enzyme 

 element of the reaction. The following 

 provisional hypothesis is built around 

 these considerations: 



First, we will suppose that color de- 

 pends on the rates of production or of 

 potency of two enzymes. Enzyme I is 

 essential to the production of any 

 color, but by itself only produces 

 yellow. Enzyme II is supplementary 

 to enzyme I, producing no effect by 

 itself. The compound enzyme, I-lt, 

 produces a darker kind of pigment 

 than enzyme I alone, viz., sepia. En- 

 zyme I-II is also more efficient than 



WRIGHT 



enzyme I in another way. It produces 

 sepia pigment even when enzyme I is 

 at too low a potency to produce any 

 yellow by itself. Above the level at 

 which enzyme I produces effects, the 

 two enzymes, I and I-II, compete in 

 the oxidation of chromogen. Chromo- 

 gen which is oxidized by enzyme I to 

 yellow pigment is incapable of further 

 oxidation to black. In the mixture the 

 presence of the relatively pale yellow 

 color serves mainly to dilute the color 

 of the hair. This production of yellow 

 reduces the amount of dark pigment 

 and the apparent intensity of color, 

 both by reducing the amount of en- 

 zyme I which can unite with II to 

 form the enzyme for black produc- 

 tion and also by using up chromogen 

 which would otherwise become black. 

 That tyrosinase is exhausted in the 

 production of pigment has been shown 

 by Gortner," who also quotes experi- 

 ments by Roques (1909) to the same 

 effect. 



i4Gortner, R. A., 

 Biol, ajid Med., 9:1. 



1912. Proc. Soc. Exp. 



CYTOPLASM 







CHROMOGEN 



NUCLEUS 



1 



ENZYMES 



Fig. 1. 



I. Basic enzyme for color produc- 

 tion. Acting alone on chro- 

 mogen, produces yellow. 



II. Supplementary to I. 



Has no effect alone, on chro- 

 mogen or yellow pigment. 



I-II. Oxidizes chromogen to sepia. 

 Effective below threshold 

 level for enzyme I alone. 

 Above this level I and I-II 

 compete. 



