Section 40
Chapter 39,167

Activation of lecithin-cholesterol acyltransferase by apolipoprotein D: comparison of proteoliposomes containing apolipoprotein D, A-i or C-i

Steyrer, E.; Kostner, G.M.

Biochimica et Biophysica Acta 958(3): 484-491


ISSN/ISBN: 0006-3002
PMID: 3124886
DOI: 10.1016/0005-2760(88)90235-4
Accession: 039166352

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To study the activation of lecithin-cholesterol acyl transferase (LCAT) (phosphatidylcholine:sterol O-acyltransferase, EC by apolipoprotein D in comparison to apolipoproteins A-I and C-I, proteoliposomes with a phosphatidylcholine/free cholesterol molar ratio of 24:1, containing 10-300 micrograms/ml of apolipoproteins were used. The proteoliposomes were prepared by the cholate dialysis technique. In all proteoliposome preparations we found rouleaux structures and stacked discs. The particles formed with apolipoprotein A-I were the most homogeneous, followed by apolipoprotein D- and apolipoprotein C-I-containing particles. Apolipoprotein A-I was the most potent LCAT activator in our system followed by apolipoproteins C-I and D. The fractional esterification rate observed with apolipoprotein D-containing substrates amounted to 15-48% that of apolipoprotein A-I-containing ones. Neither apolipoprotein A-I- nor C-I-containing proteoliposomes gave linear reaction kinetics with LCAT. Even during the first 15-30 min of incubation, the kinetics deviated strikingly from linearity at all apolipoprotein concentrations. In contrast, proteoliposomes containing apolipoprotein D exhibited linear reaction kinetics up to 60-90 min. At low apolipoprotein A-I concentrations (5 micrograms/ml), the addition of apolipoprotein D to the incubates resulted in significantly higher esterification rates as compared to substrates containing apolipoprotein A-I only. This was not the case using substrates with high apolipoprotein A-I concentrations (50 micrograms/ml). From our results we speculate that apolipoprotein D may have some stabilizing effect on the enzyme LCAT.

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