Relipidation of Human Plasma Apolipoproteins with Phospholipids.

摘要

Relipidation of three major apolipoproteins with two phospholipids,lecithin,and lysolecithin were studied. Preparative ultracentrifugation,electron microscopy,and gradient gel electrophoresis were used to characterize the complexes formed. Circular dichroism and fluorescence were used to gain insight into the effect of lysolecithin on the conformation of these apolipoproteins. Lecithin apparently relipidated A-I during incubation without sonication,forming two different complexes at all ratios of A-I and lecithin. One complex had a low lipid:protein ratio and the other complex had a high lipid:protein ratio. The complex with the low lipid:protein ratio apparently had a molecular weight less than 120,000;the other had a high molecular weight,greater than 900,000. Electron microscopy,however,indicated that various classes of complexes with different sizes were formed in each mixture of lecithin and A-I. In the presence of lysolecithin, A-I was relipidated with lecithin in a markedly different way than in the absence of lysolecithin. Based on the results of preparative ultracentrifugation it appeared as if only one class of complexes was formed during incubation of mixtures of lecithin, lysolecithin,and A-I. In no mixture did there appear to be distinct classes with different densities. By electron microscopy,particles of specific shapes could be discerned in specificmixtures of lecithin, lysolecithin,and A-I. These results were summarized by means of a ternary phase diagram showing the relation of mixture composition to the shapes of the mixed micelles seen in a mixture with a particular ratio lecithin:lysolecithin:A-I. An hypothesis to explain the effect of lysolecithin on the relipidation of A-I was developed. (ERA citation 01:026567)