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

Daniel A. Lambert, Alberico L. Catapano, Louis C. Smith, John T. Sparrow, Antonio Gotto

Research output: Contribution to journalArticle

19 Scopus citations

Abstract

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-IIII1 had a similar inhibitory effect on LPL. Inhibition with apoC-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 μM) and apo C-III1 (0-1.0 μM) 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 μM. No further activation was obtained between 0.06 and 0.30 μ M. Higher concentrations decreased LPL activity. Apo C-III1 (0.1 μM) 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 μM) required higher apo C-II concentrations (0.30 μM instead of 0.06 μM) 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 μM 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 μM), 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 that hyperlipoproteinemia seems to be more likely due to overproduction of VLDL, than to a decrease in lipoprotein lipase activity.

Original languageEnglish (US)
Pages (from-to)205-212
Number of pages8
JournalAtherosclerosis
Volume127
Issue number2
DOIs
StatePublished - Dec 20 1996

Keywords

  • apolipoproteins
  • lipoprotein lipase
  • protein cofactors

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine

Fingerprint Dive into the research topics of 'Effect of the apolipoprotein C-II/C-III<sub>1</sub> ratio on the capacity of purified milk lipoprotein lipase to hydrolyse triglycerides in monolayer vesicles'. Together they form a unique fingerprint.

Cite this