Processing of Apolipoprotein B-100 of Human Plasma Low Density Lipoproteins by Tissue and Plasma Kallikreins
Human plasma low density lipoporteins (LDL) are the major carriers of cholesterol and cholesteryl esters in the circulation. Their increased levels correlate positively with increased risk of coronary artery disease. LDL contain a single major apolipoprotein of apparent molecualr weight (Mr) = 550,000, designated apolipoprotein B-100 (apoB-100), and ins ome LDL preparations, minor components termed apoB-74 (410,000) and apoB-26 (145,000). The structural relationship of the apoB-74 and -26 proteins to the apoB-100 has remained obscure and their roles in cholesterol metabolism are unknown. In the present study, we show that the addition of kaolin to plasma anticoagulated with EDTA induces the proteolytic cleavage of apoB-100. As a result, two apoB peptides are produced with Mr indistinguishable from plasma apoB-74 and -26. The specific cleavage of apoB-100 was mimicked in vitro by purified human plasma and tissue kallikreins. In contrast, thrombin, factor Xa, plasmin, trypsin, and chymotrypsin did not produce these peptides when incubated with LDL. The findings of the study suggest that apoB-74 and -26 are proteolytic fragments of apoB-100 and that the endogenous protease has a kallikrein-like specificity for DLD-apoB-100. The role of plasma and tissue kallikreins in cholesterol metabolism remains to be determined.
KeywordsNephrotic Syndrome Apparent Molecular Weight Tissue Kallikrein Plasma Kallikrein Goat Antiserum
Unable to display preview. Download preview PDF.
- 12.J. M. Gershoni and G. E. Palade, Protein blotting: Principles and applciations, Anal. Biochem., 131: 1–15 (1983).Google Scholar
- 15.T. S. Paskhina, L. R. Polyantseva, A. V. Krinskaya, T. P. Egorova, V. Ph. Nartikova, I. M. Karmansky, and R. I. Yakubovskaya, Components of KKKK system in plasma and edematous fluids of patients with nephrotic syndrome (NS): Compensatory and pathogenetic role of kinins in nephrotic syndrome, Adv. Exp. Med. Biol., 156B: 1119–1125 (1983).PubMedGoogle Scholar
- 17.H. Nolly and M. C. Lama, Vascular kallikrein: A kallikrein-like enzyme present in vascular tissue of the rat, Clin. Sci. (Lond.), 63: 249s–251s (1982).Google Scholar