The metabolism of very low density lipoprotein proteins. II. Studies on the transfer of apoproteins between plasma lipoproteins.

Abstract

Abstract 1. 1. Apolipoprotein-glutamic acid (apoLP-Glu) and apolipoprotein-alanine (apoLP-Ala), small molecular weight apolipoproteins, readily transfer in vitro from very low density lipoprotein to other lipoproteins. Their transfer to high density lipoprotein always exceeds that to low density lipoproteins, and is proportional to the concentration of lipoproteins present in the incubation mixture. A similar transfer of radioactivity occurs in vivo , and is proportional to both plasma triglyceride and high density lipoprotein cholesterol levels. The transfer of apoLP-Glu and apoLP-Ala between very low density and high density lipoproteins is bidirectional, and thus represents, at least in part, an exchange phenomenon. In contrast, the apoprotein moiety of low density lipoprotein does not participate in this type of transfer. 2. 2. Apolipoproteins can be separated into groups following their reassociation properties with lipids and lipoproteins. ApoLP-Glu and apoLP-Ala reassociate with all plasma lipoproteins, predominantly very low density and high density lipoprotein. Apolipoprotein-glutamine 1 (apoLP-Gln 1 ) and apolipoprotein-glutamine 2 (apoLP-Gln 2 ) reassociate primarily with their parent lipoprotein, high density lipoprotein. Representative proteins of both groups however, reassociate with lipid (lecithin or triglyceride). The recombination of apoproteins with lipoproteins thus may be specific and involve a process of “recognition” of the lipoprotein by the apoprotein. This specificity may not be involved in the simple recombination of apolipoproteins and lipids. These observations may explain the distribution of apoproteins among plasma lipoproteins and provide insight into their metabolic fate.