Effect of the apolipoprotein C-II/C-III1 ratio on the capacity of purified milk lipoprotein lipase to hydrolyse triglycerides in monolayer vesicles

• Published in: Atherosclerosis 1996-12, Vol.127 (2), p.205-212
• Main Authors: LAMBERT, D. A, CATAPANO, A. L, SMITH, L. C, SPARROW, J. T, GOTTO, A. M
• Format: Article
• Language: English
• Subjects: Animals; Apolipoprotein C-II; Apolipoprotein C-III; Apolipoproteins C - pharmacology; Biological and medical sciences; Biological Transport; Cattle; Chylomicrons - drug effects; Chylomicrons - physiology; Fundamental and applied biological sciences. Psychology; Hydrolysis - drug effects; In Vitro Techniques; Lipids. Glycolipids; Lipoprotein Lipase - drug effects; Lipoprotein Lipase - metabolism; Metabolisms and neurohumoral controls; Milk Proteins - metabolism; Triglycerides - metabolism; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0021-9150; 1879-1484
• DOI: 10.1016/S0021-9150(96)05955-2

The effect of the apolipoprotein C-II/C-III1 ratio on the capacity of purified bovine milk lipoprotein lipase to hydrolyse triglycerides was measured in a controlled model of pyrene-labeled nonanoyltriglycerides (1-2 ditetradecyl 3-pyrene nonanoyl glyceride) monolayer vesicles. Monolayer was composed of triglycerides, a non-hydrolysable phospholipid ether and cholesterol, a model system where the quality of the interface can be controlled. LPL released fatty acids from pyrene-triglycerides which were transferred from the lipoprotein structure to albumin. This transfer induces a decrease in the excimer production and in the excimer fluorescence intensity. Apolipoprotein C-II and C-III0 and C-III1 were purified from apolipoprotein VLDL. The 2 fragments, C-III1 A (peptide 1-40) and C-III1 B (peptide 41-79), were obtained after thrombin cleavage. Apolipoproteins C-III0 and C-III1 had a similar inhibitory effect on LPL. Inhibition with apo C-III0 or apo C-III1 was 85% of full LPL activity without inhibitor: Apo C-III1 B inhibited 62% of basal activity. It was 27% less effective than apo C-III1. Fragment C-III1 A did not inhibit LPL. The effect of change in both apo C-II (0-0.6 microM) and apo C-III1 (0-1.0 microM) on triglyceride hydrolysis shows the importance of the apo C-II/C-III1 ratio for the release of free fatty acids from triglycerides by LPL. The activating effect of apo C-II in the absence of the apo C-III inhibitor was maximal at 0.06 microM. No further activation was obtained between 0.06 and 0.30 microM. Higher concentrations decreased LPL activity. Apo C-III1 (0.1 microM) decreased the maximum activation by apo C-II from 0.0196 to 0.063 nmol/min/nmol LPL. Higher concentrations of apo C-III1 (0.1-0.5 microM) required higher apo C-II concentrations (0.30 microM instead of 0.06 microM) for maximal activation than when apo C-III1 was absent. The activity of the enzyme without apo C-II was decreased by 65% by 0.12 microM apo C-III1. Increasing the apo C-II/apo C-III1 ratio from 0.1 to 1, increased the activation of the enzyme by a given apo C-II concentration. Moreover, for a given apo C-II/C-III1 ratio, the LPL activation increased with the apo C-II concentration (between 0 and 0.010 microM), until a plateau was reached. This is important, as the change in the C-II/C-III1 ratio is not the only factor affecting LPL activity, and inhibition by apo C-III1 also depends on the overall quantity of apolipoproteins. Extrapolation of these results suggests tha