Association of lysolecithin acyltransferase with the high density lipoproteins and its activation by the low density lipoproteins in normal human plasma

Incubation of intact platelets from Sinclair(S-1) miniature swine with 32P-labeled lysophosphatidylcholine (lyso PC) indicated the presence of an active lysophospholipase with a pH optimum of 8.0 for hydrolysis of the substrate. However, lyso PC was incorporated into the membrane phosphatidylcholines by the acyltransferase pathway upon addition of ATP, Mg++ and CoA to the platelet suspension. These results suggest that intact platelets are able to resist the cytotoxic effects of lyso PC in plasma, and the phospholipids in platelet membranes are not readily affected by the lipid environment of the plasma. The acyltransfer reaction apparently is saturated with endogenous free fatty acids since arachidonic acid added exogenously did not further enhance the incorporation activity. Neither the acyltransferase nor the lysophospholipase activity was affected by Ca++, but divalent metal ions such as Zn++ inhibited the lysophospholipase activity. Cholesterol but not cholesteryl esters elicited a biphasic effect on both enzymes, stimulating at low concentration but inhibiting at a cholesterol to lyso PC ratio greater than 1. Serum albumin inhibited the lysophospholipase but gave a small biphasic effect to the acyltransferase.

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Metabolism of lysophosphatidylcholine by swine platelets

Chen

White

Tumbleson

et al. 1985

Lipids

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Increased lysolecithin acyltransferase activity in the plasma of type II hyperlipoproteinenic patients

Subbaiah

Ogilvie

1984

Lipids

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Lecithin-cholesterol acyltransferase (LCAT) in human plasma has been shown to acylate lysolecithin to lecithin in presence of low density lipoprotein (LDL). To determine the physiological importance of LDL in activating lysolecithin acyltransferase (LAT) activity, we assayed the LAT activity in 18 hypercholesterolemic (Type II) patients and 15 control subjects. The enzyme activity was about 60% higher in the patients compared with the controls. On the other hand, the LCAT activity, measured by 2 different procedures, as well as enzyme mass, determined by radioimmuno assay, were comparable in the controls and hypercholesterolemics. The LAT activity was highly correlated with LDL levels in the plasma, but the LCAT activity and the enzyme mass had no correlation with the LDL levels. These results show that the plasma LDL is the rate-limiting activator of the enzyme, and pathological conditions, resulting in higher LDL levels, also cause higher LAT activities.

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Phosphatidylcholine formation from exogenous lysophosphatidylcholine in isolated hamster heart

Savard

Choy

1982

Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metaboli

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Association of lysolecithin acyltransferase with the high density lipoproteins and its activation by the low density lipoproteins in normal human plasma

Cited by 14 publications

References 10 publications

Metabolism of lysophosphatidylcholine by swine platelets

Metabolism of lysophosphatidylcholine by swine platelets

Increased lysolecithin acyltransferase activity in the plasma of type II hyperlipoproteinenic patients

Phosphatidylcholine formation from exogenous lysophosphatidylcholine in isolated hamster heart

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