Studies on the protein composition of human serum very low density lipoproteins with particular reference to the presence or absence of late pre-beta lipoprotein (Lp beta).

The amount of tetramethylurea and isopropanol soluble protein, total protein, triglycerides and cholesterol was determined in very low density lipoprotein (VLDL) showing either pre-beta mobility, or combined pre-beta and late pre-beta (Lp beta) or beta-mobility from twenty-two different sera. The ratios cholesterol to triglyceride of the VLDL preparations varied between 0.30 and 1.75. A very strong positive linear correlation between soluble protein and triglycerides over the whole range of VLDL preparations was obtained. There was no difference between sera with and without Lp beta for this relationship. When apolipoprotein B, was plotted against triglycerides, a weak correlation was obtained, and VLDL preparations without Lp beta separated into a group below the regression line, indicating that Lp beta is triglyceride poor in relation to apolipoprotein B. The corresponding plot against cholesterol gave a better correlation but with an even distribution of values of VLDL with and without Lp beta. Total and soluble protein put against cholesterol showed a pronounced tendency of VLDL with pure pre-beta mobility and those with Lp beta mobility to separate into groups, demonstrating that Lp beta is cholesterol rich relative to protein. The findings indicate that Lp beta-containing VLDL may represent the presence of a partly degraded VLDL.