DEGRADATION OF HUMAN APOLIPOPROTEIN B-100 BY APOLIPOPROTEIN(A)

Human plasma low density lipoproteins (LDL) contain a very high molecular weight protein termed apoB-100 (M(r) = 550,000). In many samples of LDL, minor components designated as apoB-74 (M(r) = 407,000) and apoB-26 (M(r) = 145,000) are present. It has been shown that they can arise as a result of proteolytic degradation of apoB-100. Our earlier studies demonstrated that the active forms of lipoprotein(a) (LP(a)) and apolipoprotein(a) (apo(a)) possess proteolytic activity. In the present study we investigated the possibility of apoB-100 degradation in the presence of activated apo(a). LDL were incubated with the purified apo(a) and analyzed by SDS-polyacrylamide gel electrophoresis. It was found that apoB is cleaved by apo(a) with formation of proteolytic fragments including B-74 and B-26. The physiological significance of apoB degradation under the action of apo(a) is considered.