The fate of cholesteryl esters in human serum incubated in vitro at 38°

• 1.

  1. Following the incubation of nonlipemic human serum (serum glyceride concentration, 49 mg%) at 38° for 36 h, the major lipoprotein species (S_f 20-10⁵, S_f 0–20, high-density lipoproteins) have been isolated ultracentrifugally and their lipid compositions determined. In all three lipoprotein species, the molar concentrations of cholesterol and phospholipids decrease, while those of the cholesteryl esters increase. The data indicate that during the course of the incubation some of the cholesteryl esters are released from the S_f 0–20 lipoproteins and, subsequently, are associated with the S_f 20-10⁵ lipoproteins and the high-density lipoproteins.

• 2.

  2. Although the total glyceride content in the serum remains constant, it decrease in the S_f 20-10⁵ lipoproteins and increases in the high-density lipoproteins and the S_f 0–20 lipoproteins. The observed reduction in the S_f 20-10⁵ lipoprotein is attributed to the transfer of glyceride to the other lipoproteins during incubation.

• 3.

  3. The fatty acid distributions to the glyceride and cholesteryl ester fractions have been determined by gas-chromatographic techniques. Significant changes are observed only in the glyceride fatty acids of the S_f 20-10⁵ lopoproteins.