112 



E. S. GUZMAN BARRON 



In condensation reactions where two substrates take part in the re- 

 action, as in the formation of acetylcholine, it seems that only one of 

 the substrates combines with the protein and becomes activated. Evi- 

 dence for this assumption is provided by inhibitions with competitive 

 inhibitors. For example, methyl bis (dichloroethyl) amine HCl inhibits 

 choline oxidase because of the similarity of its first transformation 

 product, ethylene imonium, to choline; it also inhibits the synthesis of 

 acetylcholine and its hydrolysis. It has no efifect on the hydrolysis of 

 tributyrin. Fluoroacetate inhibits the oxidation of acetate while it has 

 no effect on the synthesis of acetylcholine and acetylations in general 

 (Table VII). It must be concluded that in acetylations the protein 

 combines with the acetylated compound and not with the acetyl group. 



TABLE VII 



Effect of Methyl bis (Dichloroethyl) Amine (o.ooi M) and 

 Fluoroacetate (o.oi M) on Acetylations, Oxidations, and Hydrolysis. 



A number of proteins, components of enzyme systems, have been iso- 

 lated and prepared in crystalline form. Furthermore our knowledge of 

 the physical and chemical properties of proteins has considerably in- 

 creased during the last years. The time has come to use these techniques 

 for a serious study of the protein moiety of the enzyme. It is necessary 

 to know the architecture of the protein moiety of the enzyme, the spac- 

 ing of the side groups to which the substrates attach themselves, and 

 the nature of the activation of the substrate. 



The Oxidation-Reduction Systems 



In 1930 Barron and Hoffman (10) found that the catalytic power of 

 reversible oxidation-reduction dyes on cellular respiration was condi- 

 tioned by two factors: the oxidation-reduction potential of the dye 

 (Fig. i), and the permeability of the cell membrane (Table VIII). 



