130 E. S. GUZMAN BARRON 



glutarate is oxidized by sea urchin eggs. Fluoroacetate had no effect 

 on the O2 uptake. 



Cell Growth 



Our knowledge of the enzymatic reactions which take part in cellular 

 growth is meager. In general cellular growth, new protein formation, 

 takes place at the expense of aerobic oxidations except in those cells 

 deprived of cytochromes. 



Voegtlin (82), Hammett (33), and Rapkine (73) have for a long 

 time championed the importance of sulfhydryl groups in cell growth, 

 and evidence in support of this opinion is good. They have been found 

 increased in concentration in growing cells (62, 88) and growth was 

 inhibited on addition of substances which combine with — SH groups 

 (27, 34, 74, 76). It has already been pointed out that there are a large 

 number of enzymes which require the presence of — SH groups in their 

 protein moiety for activation. Destruction of these groups by oxidation 

 (x-rays, Oo, Cu), alkylations (CHJCOOH, CHJCOONH^, mustard, 

 nitrogen mustard), or mercaptide formation (Hg, Pb, Cd, Zn, Bi, As, 

 V, Sb) will produce enzyme inhibitions, an inhibition which affects 

 such high-energy yielding reactions as pyruvate oxidase, a-ketoglutarate 

 oxidase, succinoxidase, triosephosphate oxidase, adenosinetriphospha- 

 tase, malate oxidase. Sluggish oxidation-reduction systems, mostly in 

 their reduced state (glutathione, ascorbic acid), have also been found 

 abundant in cells during growth and development. These systems must 

 have for function that of keeping the — SH groups of the enzymes in 

 the reduced, physiologically active state. 



It must be recalled that ionizing radiations (63), halogenated alkyla- 

 mines (30), and mustard gas (i) inhibit mitosis. Furthermore Hevesy 

 (36) has found that the synthesis of nucleoproteins (which take part 

 in mitosis) is inhibited by x-rays. Under certain conditions enzymes 

 like adenosinetriphosphatase from aged myosin are so susceptible to 

 ionizing radiations that amounts as small as ir produce inhibition 

 (Table XI). The inhibiting effect of x-rays may well indicate that 

 some enzyme necessary for the synthesis of nucleoproteins requires 

 — SH groups for its activity, groups which are oxidized by the OH and 

 O2H radicals, and H2O2 produced during the irradiation of water. The 

 inhibiting effect of mustard gas and of nitrogen mustard might also be 

 due to combination of these substances with the — SH groups. The fact 

 that lewisite produces no effect (i) is no serious objection, because 



