ENZYMES CONCERNED WITH DIGESTION OF LIPIDS 17 



The action of liver esterase in hydrolyzing triacetin is stimulated to the 

 extent of 50% by the addition of amino acids such as L-aspartic, L-glutamic, 

 or L-histidine, while the hydrolysis of butylbutyrate is not augmented by 

 these amino acids." Moreover, Yamamoto" showed that the free amino 

 group of L-aspartic acid is the significant group in accelerating the hydrolysis 

 of triacetin. The liver esterases (ali-esterases) are highly sensitive to in- 

 hibition by various alkyl phosphate derivatives such as E600. They can 

 be selectively inhibited by tri-o-cresyl phosphate. 100 In the latter case, 

 Mendel and Myers 101 reported that the order of sensitivity of esterases is as 

 follows : serum tributyrinase > pseudocholinesterase > true cholinesterase > 

 brain tributyrinase. 



Myers and Mendel 100 have reported that the ali-esterases of liver and 

 phospholipase are inhibited to the extent of 60 to 70% by 10 -2 M atoxyl, 

 while the lipase activity is not significantly affected either by the phosphate 

 derivatives or by atoxyl in concentrations which inhibit ali-esterase activ- 

 ity. The atoxyl-resistant part of serum lipase varies in different animals, 

 having a maximum of approximately 80%. Highest values were found for 

 sera of the rat, horse, and guinea pig and the lowest in that of man. 102 

 Irrgang and Dustmann 102 suggest that a rise in atoxyl-resistant lipase in 

 human serum is an indication of resistance toward carcinoma. Resistance 

 to quinine, which is a characteristic of esterases rather than of lipases, was 

 also found to be as high as 82% for lipase in some species. The extent of 

 atoxyl-resistant and of quinine-resistant lipase is characteristic of species. 102 



Nachlas and Seligman 103 reported that kidney and liver esterases are 

 inhibited by eserine, sodium arsenilate, and fluoride. Of these, only 

 eserine inhibits lipase. Taurocholate was also shown to decrease esterase 

 activity slightly, while it augments that of lipase. Liver esterase is more 

 resistant to alkali treatment at pH 9.2 to 11.0 than lipase, which is de- 

 stroyed under these conditions." Connors and associates 104 reported that 

 a highly concentrated liver esterase preparation had a pH optimum of 8.0 

 in borate with methyl butyrate as a substrate; the temperature coefficient 

 was found to be 1.28, the energy of activation 4430 calories per mole and the 

 Michaelis-Menten constant 0.022 M. 



d. Factors Altering the Action of Esterases. Esterases are most effec- 

 tive in splitting simple esters of short-chain acids. 103 The length of the 



99 T. Yamamoto, J. Biochem. {Japan), 38, 335-341 (1950). 



100 D. K. Myers, and B. Mendel, Biochem. J., 53, 16-25 (1953). 



101 B. Mendel and D. K. Myers, Biochem. J., 53, xvi (1953). 



102 K. Irrgang and I. Dustmann, Biochem. Z., 322, 520-525 (1952). 



103 M. M. Nachlas and A. M. Seligman, J. Biol. Chem., 181, 343-355 (1949). 



104 W. M. Connors, A. Pihl, A. L. Dounce, and E. Stotz, J. Biol Chem., 184, 29-36 

 (1950). 



