An abnormal triglyceride-rich lipoprotein carrying excess apolipoprotein C-II

The polypeptide composition of a variant lipoprotein (d less than 1.006) carrying a relative excess of apolipoprotein C-II has been characterised by polyacrylamide gel electrophoresis and isoelectric focussing. The apo-C peptides of the variant lipoprotein contained 45.2 +/- 1.3 (n = 9) % of apo C-II compared with 21.5 +/- 5.4 (n = 30) % for hypertriglyceridaemic controls. The variant lipoprotein activated purified bovine milk lipoprotein lipase normally, but was an inefficient substrate for this enzyme as assessed by direct release of fatty acids from the lipoprotein or by a substrate competition assay. Electron microscopy revealed the variant lipoprotein as non-spherical flattened particles compared with the more spherical appearance of control triglyceride-rich lipoproteins. We suggest that the relative proportion of apo C peptides associated with the lipoprotein particle may be critical for optimal enzyme-substrate interaction.