The metabolism of very low density lipoprotein proteins I. Preliminary in vitro and in vivo observations

During the first 24 h after injection of 125I-labeled very low density lipoprotein to humans, the decay rate of low densitylipoprotein apoprotein from very lowdensity lipoproteins was faster than that of apolipoprotein glutamic acid, apoipoprotein alanine1 and apolipropoteinAlanine2.

Abstract

1. The metabolic fate of the apoproteins of very low density lipoprotein was studied by labeling the protein moiety of very low density lipoprotein with 125I. 46–57% of the label bound to low density lipoprotein (d 1.019–1.063) apoprotein and 31–44% attached to apolipoprotein glutamic acid, apolipopotein alanine1 and apolipropotein alanine2. Following in vitro incubation of labeled very low density lipoprotein in plasma, or 10 min after intravenous injection into humans, labeled apolipoprotein glutamic acid, apolipoprotein alanine1 and apolipropotein alanine2 transferred to other lipoproteins, mainly high density lipoprotein. Low density lipoprotein apoprotein, in contrast, was confined to the very low density lipoprotein density range under these conditions. 2. During the first 24 h after injection of 125I-labeled very low density lipoprotein to humans, the decay rate of low density lipoprotein apoprotein from very low density lipoprotein was faster than that of apolipoprotein glutamic acid, apolipoprotein alanine1 and apolipoprotein alanine2. During this interval, radioactivity accumalated first in a lipoprotein of intermediate density (d 1.006–1.019) and later in low density lipoprotein (d 1.019–1.063). It is suggested that apolipoprotein glutamic acid, apolipoprotein alanine1 and apolipoprotein alanine2 exchange readily between lipoproteins, but the low density lipoprotein apoprotein moiety of very low density lipoprotein moves unidirectionally from very low density lipoprotein to low density lipoprotein through a lipoprotein of intermediate density (d 1.006–1.019).