CYTOPLASM 



CHROMOGEN 



NUCLEUS 



<3 



n 



n 



ENZYMES 



I. Basic enzyme for color produc- 

 tion. Acting alone on chro- 

 mogen, produces yellow. 



II. Suj)plcinentary to I. 



Has no effect alone, on chro- 

 mogen or yellow pigment. 



( )xi(lizes chromogen to sepia. 

 H)ffectivc below threshold 

 level for enzyme I alone. 

 Above this level I and I-II 

 compete. (Fig. 8.) 



tictilar ones oxidized dejjcndin^ on ihe 

 character of the enzymes ]jresent, and 

 finally that hereditary differences in 

 color are due to hereditary differences in 

 the enzyme element of the reaction. 

 The followinj^ ])rovisional hy])othesis is 

 built around these considerations: 



First, we will suppose that color 

 depends on the rates of production or of 

 potency of two enzymes. Enz\Tne I is 

 essential to the ]jrodtiction of any color, 

 but by itself only ])roduces yellow. 

 Enzyme II is supplementary to enz\me 

 I. ])roducinj^ no effect l)y itself. Th:' 

 Cf^mpound enzyme. III, j^rodtices a 

 darker kind of jjigment than enzyme I 

 alone, viz., sepia. EnzvTnc I-II is also 

 more efficient than enzyme I in another 

 way. It produces sepia ])i}^ment even 

 when enzNTne I is at too low a ])otency 

 to produce any yellow by itself. Above 

 the level at which enzyme I jjroduces 

 effects, the two enzymes, I and III, 

 comi)ete in the oxidation of chromogen. 

 Chromogen which is oxidized by enzyme 

 I to yellow pij^ment is incapable f)f 

 further oxidation to black. In the 

 mixture the i)resence of the relatively 

 l)ale yellow color serves mainly to 

 dilute the color of the hair. Thi.-; 



prtxluction of yellow reduces the amount 

 of dark ])ij.^ent and the apparent 

 intensity of color, both by reducin}.!; the 

 amount of enzyme I which can imite 

 with II to form the enzyme for black 

 ])roduction and also by usinj.^ up chromo- 

 ^vn which would otherwise become 

 black. That tyrosinase is exhausted in 

 the production of pigment has been 

 shown by Gortner,^* who also quotes 

 exiK'riments by Roques (1Q09) to the 

 same effect. 



There are three i)oints in the dia- 

 j.,'ram (Fig. 8) at which jjhysiological 

 processes may affect color-j^rodtiction 

 indei)endently, viz., by infltience on 

 chromogen, on enz\Tne I, and enzyme II. 

 In the first two cases color should be 

 modified regardless of its quality. But 

 as there is as yet no experimental 

 evidence that genetic factors determine 

 variations in the chromogen element it 

 will be convenient at present to consider 

 all such cases as dtie to influence on 

 enzNTne I. 



The relations between black, red and 

 white in this scheme are obvious. 

 Inhibition of enzyme II when enzyme I 

 is present gives red. Inhibition of 

 enzyme I gives while regardless of 



'Hlortncr, R. .\.. I'M 2. /'roc. Sor. l-.xp. Biol, mil MrL. 0: 1. 

 22« 



