Cholesterol esterases. III. Occurrence and characteristics of cholesterol esterase of serum

1950 Journal of Biological Chemistry  
Sperry and Brand (1) have discussed the possible importance of cholesterol esterase in the absorption and metabolism of cholesterol. While earlier work had suggested that whole blood had cholesterol esterase activity, Sperry (2) was the first to report esterifying activity in serum. In a series of studies (l-4), Sperry and coworkers reported that esterification of the free cholesterol occurred when human or dog serum was incubated alone, that the reaction was absent in serum heated for 1 hour
more » ... heated for 1 hour at 55-GO", and that the optimum pH for the reaction was about 8. It was found that bile salts had a marked effect on this esterification reaction. In human serum, as the bile salt concentration was increased, the esterification decreased, and, above a certain concentration of bile salts, there was neither esterification nor hydrolysis. With dog serum there was a decrease in esterification as the bile salt concentration was increased until a point was reached at which no esterification or hydrolysis occurred. With amounts of bile salts above this level the cholesterol esters of dog serum were hydrolyzed more or less in proportion to the concentration of bile salt until with large amounts complete splitting had occurred. Two recent reports (5, 6) have described the preparation of substrate mixtures, suitable for studying the hydrolyzing and esterifying cholesterol esterase systems, and the employment of these mixtures in the characterization of the enzyme in pancreatin. The present report gives the results of an investigation of the occurrence of cholesterol esterase in the serum of five species, namely, human, dog, rat, rabbit, and guinea pig. When these were tested according to our procedures (5, G), only dog serum exhibited cholesterol esterase activity. Further experiments demonstrated that the enzyme in dog serum was like that previously characterized in pancreatin (5, 6). Inasmuch as our results did not confirm the reports of Sperry and coworkers in respect to the cholesterol esterase activity of human serum, it seemed desirable to test human and dog sera under conditions closely simulating those employed in the earlier studies. These *
pmid:15436508 fatcat:ayy77vulizckbncs4e2wg3kfiq