KINETIC EVIDENCE FOR PHOSPHATIDYLETHANOLAMINE AND TRIACYLGLYCEROL AS PREFERENTIAL SUBSTRATES FOR HEPATIC LIPASE IN HDL SUBFRACTIONS - MODULATION BY CHANGES IN THE PARTICLE SURFACE, OR IN THE LIPID CORE

被引:24
作者
AZEMA, C [1 ]
MARQUESVIDAL, P [1 ]
LESPINE, A [1 ]
SIMARD, G [1 ]
CHAP, H [1 ]
PERRET, B [1 ]
机构
[1] HOP PURPAN,INSERM,U326,F-31059 TOULOUSE,FRANCE
关键词
HDL; Hepatic lipase; Phospholipid; Triacylglycerol;
D O I
10.1016/0005-2760(90)90096-G
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Human HDL subfractions, HDL2 (d: 1.085-1.125) and HDL3 (d: 1.125-1.19) labelled with 2-[14C]linoleoylphos-phatidylethanolamine and tri-[3H]oleoylglycerol, were incubated with partially purified hepatic triacylglycerol lipase, isolated from human post-heparin plasma. Kinetics of hydrolysis of these two HDL-lipid substrates were followed and were compared to those previously obtained on phosphatidylcholine (G. Simard et al (1989) Biochim. Biophys. Acta 1001, 225-233). (1) The apparent Km obtained for HDL-triacylglycerol was half that for HDL-phosphatidylethanolamine, but the estimated Vmax was higher for the latter. Hence, despite a lower affinity, more molecules of phosphatidylethanolamine than of triacylglycerol were found hydrolysed. A strong correlation was observed between the hepatic lipase activity added and the maximal degradation rates for phosphatidylethanolamine measured in HDL2 and HDL3. (2) A linear relationship was observed in both HDL2 and HDL3 between the respective degradations of the two substrates. The number of phosphatidylethanolamine molecules hydrolysed exceeded that of triacylglycerol by 30% in HDL2 and by 70% in HDL3. HDL2 were 2- and 4-times more reactive than HDL3 for the hydrolysis of phosphatidylethanolamine and triacylglycerol, respectively, taking the Vmax/Km ratio as an indicator of catalytic efficiency. In both HDL subfractions, the calculated Vmax/Km value was 30-50-fold higher for PE and TG than for PC. (3) HDL particles were modified either on their surface by selective enrichment in free cholesterol or in their inner-core by replacement of esterified cholesterol by triacylglycerol in presence of a source of neutral lipid transfer activity. A mild cholesterol enrichment stimulated the phosphatidylethanolamine and triacylglycerol reactivities by 30-60% towards hepatic lipase, whereas increasing the triacylglycerol concentration in HDL was followed by a proportional increase in the amounts of triacylglycerol hydrolysed with no effect on phospholipid degradation. © 1990.
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页码:73 / 80
页数:8
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