ENZYMES CONCERNED WITH DIGESTION OF LIPIDS 31 



work of Alles and Hawes, 191 - 192 Richter and Croft, 193 Mendel and Rudney, 186 

 and of Zeller and associates. 185,194 



(d) Properties of Cholinesterases. a'. General Properties of Cholinester- 

 ases: Marked variations in properties obtain between the different types 

 of cholinesterases. The differences between the e-type and the s-type are 

 summarized in Table 2. 



It is known that true cholinesterase is inhibited by an excess of substrate 

 while the pseudo form is not affected. When an increasing concentration 

 of salt is added to the medium, the optimum acetylcholine concentration is 

 shifted to higher levels. Although the higher salt levels decrease the affin- 

 ity of the enzyme for acetylcholine, at the same time they potentiate the 

 hydrolytic activity of the enzyme toward acetylcholine. According to 

 Myers 195 this behavior is explained on the basis of a dispositional enzyme 

 active center, which may be either its "anionic" grouping, or its "ester" 

 grouping, or both. 196 In the case of pseudocholinesterase, the active 

 center is also dipositional; however, the affinity of acetylcholine for the 

 pseudo-enzyme appears to depend mainly upon the ester structure of the 

 molecule. 195 Elley and Stone 197 have suggested that, since acetylcholine 

 is a "low-energy" compound, the main point of adsorption of pseudoester- 

 ase is on the ester group of the acetylcholine molecule. They base their 

 conclusion on the demonstration of a similarity between the non-enzymic 

 hydrolysis of acetylcholine bromide and of non-ionic esters such as methyl 

 acetate. 



Augustinsson, 198 likewise, pointed out that the effect of substrate con- 

 centration varies with the type of cholinesterase. Thus, the cholinesterases 

 present in all conductive tissues tested, and in erythrocytes, show a 

 rather sharp optimum concentration of acetylcholine. The optimum 

 substrate concentrations are quite similar, for most choline esters, although, 

 in some cases, they may differ. 198 On the other hand, the cholinesterases 

 present in serum exhibit the usual dissociation curve. Triacetin, for 

 example, is split at a slow rate in low concentration and at a high rate when 

 present in high concentration. The velocity of the reaction with the 

 pseudo-enzyme decreases with the increases in molecular weight of the 



191 G. A. Alles and R. C. Hawes, /. Biol. Chem., 183, 375-390 (1940). 



192 R. C. Hawes and G. A. Alles, /. Lab. Clin. Med., 26, 845-853 (1941). 



193 D. Richter and P. G Croft, Biochem. J., 36, 746-757 (1942). 



194 E. A. Zeller, Helv. Chim. Acta, 25, 1099-1110 (1942). 

 196 D. K. Myers, Arch. Biochem., 37, 469-487 (1952). 



196 D. K. Myers, Arch. Biochem., 31, 29-40 (1951). 



197 D. D. Elley and G. S. Stone, Biochem. J., 49, xxx (1951) 



198 K. B. Augustinsson, Arch. Biochem., 23, 111-126 (1949) 



