Physical-chemical changes in serum lipoproteins during incubation of human serum

Abstract

Incubation of human serum for 24 h at 37° resulted in a marked shift in the ultracentrifugal distribution of the high-density lipoprotein (HDL) fraction. The serum concentrations of the F° 1.20 0–3.5 (HDL 3) decreased while those of the F° 1.20 3.5–9.0 (HDL 2) increased. Inhibition of serum fatty acid transferase activity by p-hydroxymercuribenzoate did not inhibit the incubation-induced change in HDL distribution. A significant reduction in the protein content of the HDL, isolated from incubated serum, was detected. These data suggest that the shift in HDL distribution may result from an initial dissociation of protein from HDL 3 followed by an association of relatively lipid-rich lipoprotein residues to give HDL 2-type lipoproteins. Small order increases in S° f rates of the major peak of the S° f 0–20 fraction were also observed, during incubation of serum, in the presence as well as in the absence of transferase activity. The magnitude of the increase in s f 5 rate was found to be directly related to the level of S° f 20–400 lipoproteins in the serum and to be greater in the presence of transferase activity.