Abstract
The rate and fatty acid specificity of cholesterol esterification by the blood serum of laying hens was studied in vitro.
In the laying hens, levels of free cho-lesterol in the serum and in the β-lipoprotein fraction were considerably higher, and the ratio of ester to total consequently lower, than those for the male or non-laying female birds. The latter difference in both the male and non-laying females was from 68-72% to 26-49%. The values for a-lipo-proteins, however was essentially the same in both sexes.
The fatty acid composition of cholesterol esters of laying hen serum was characterized by higher levels of saturated and monoenoic acids and lower levels of the polyunsaturated acids, as compared with the corresponding values for the male and non-laying female. These trends were especially clear in the cholesterol esters of the β-lipoprotein fraction.
The rate of cholesterol esterification by layers' whole serum in vitro was substantially slower than that of the male, the results being comparable to those obtained by in vivo experiments. However, cholesterol esteri-fying activity in serum α-lipoproteins of the laying hen was significantly higher than that in the β-lipoprotein fraction. The specific activity of newly formed cholesterol esters was again found to be heterogeneous with respect to the different fatty acid esters, as is true of the male and non-laying female. Polyunsaturated acid esters showed a high activity and saturated esters low activity -compared to that of total cholesterol esters. Although the enzyme obtained from laying hens was markedly less active in regard to saturated acids, that from the β-lipoprotein fraction did appear to have a greater esteri-fying potential for these acid esters than did the enzyme in the α-lipoprotein fraction.
Some estimation of the fatty acid speci-ficity of the serum enzyme was made. Results indicate that the sera from both male and laying female birds generally have the same specificity, but that the influence of the fatty acid used as donor must not be overlooked.
