ENZYMES CONCERNED WITH DIGESTION OF LIPIDS 19 



purification by dialysis followed by precipitation with ammonium sulfate 

 while, in the method of Kraut and Rubenbauer, U5 a protein-free prepara- 

 tion was obtained by employing adsorption following the dialysis step. 

 The preparation of Baker and King 116 was likewise a highly purified prod- 

 uct. The liver has, in general, been the source of preparations of rela- 

 tively pure esterase, since the enzyme is abundant there; when attempts 

 were made to obtain purified products from other tissues, the same general 

 procedures were employed as were used for liver. Falconer and Taylor 88 

 obtained a solution of pig fiver esterase 10 to 15% purer than whole liver. 

 Connors et al. Wi prepared an acetone-dried powder from horse liver in 

 which the esterase was concentrated by a factor of 270. In the latter case, 

 a combination of ammonium sulfate and acetone fractionations was em- 

 ployed, together with heat and heavy metal denaturations and dialysis. 



f. Esterases vs. Lipases. All the evidence points to the fact that the 

 mechanism involved in splitting the ester linkages in triglycerides is differ- 

 ent from that of the esters of monohydric alcohols. Lipases which will 

 catalyze the breakdown of triglycerides are impotent in bringing about 

 hydrolysis of simple esters. On the other hand, esterases which accelerate 

 the hydrolysis of simple esters are ineffective oh the ester linkages in tri- 

 glycerides. 



The marked differences between pancreatic lipase and liver esterases are 

 shown in a variety of ways. Thus, there is a marked contrast in the rela- 

 tive velocity constants of their action on triglycerides and simple esters. 117 

 As has already been noted, bile salts and other organic compounds which 

 activate lipases actually depress the esterases. 26 Finally, the kinetics of 

 the enzyme-substrate reactions differ for these two classes of enzymes. 117 

 While the pancreas produces a true lipase, it also elaborates at least two 

 different esterases. On the other hand, no lipase is produced in the liver, 

 although this organ does synthesize two esterases. Although the lipolytic 

 action of plasma undoubtedly originates in part from the pancreatic lipase, 

 a portion of it has the property of an esterase. 



(3) Other Lipid-Hydrolyzing Enzymes 



In addition to the enzymes included in the general classification of ester- 

 ases, a number of specific enzymes, which act on the ester linkage in a 

 limited variety of compounds, are of importance in various phases of lipid 



116 H. Kraut and H. Rubenbauer, Z. physiol. Chem., 173, 103-117 (1928). 



116 Z. Baker and C. G. King, J. Am. Chem. Soc, 57, 358-361 (1935). 



117 S. S. Weinstein and A. M. Wynne, J. Biol. Chem., 112, 641-648 (1936). 



