Chimpanzee serum lipoproteins: Isolation, characterisation and comparative aspects of the low density lipoprotein and apolipoprotein-BH

Abstract Evaluation of the serum lipoprotein profile in non-fasting, adult chimpanzees by analytical ultracentrifugation revealed a lower mean LDL level (269 mg/dl) than typical of man. The major molecular form(s) of low density lipoprotein (LDL) was then isolated in the density interval 1.024-1.050 g/ml by sequential ultracentrifugation. The physicochemical properties of chimpanzee LDL, including net surface charge as judged by electrophoresis, molecular size (220 A) by electron microscopy, and chemical composition closely resembled those of man. The antigenic structures of chimpanzee and human LDL were essentially indistinguishable, since immunodiffusion against antiserum to either the human or ape lipoprotein produced a precipitin reaction of complete identity between the two antigens. By micro-immunoprecipitation, the immunological cross-reactivity of LDL from the two species was in the range 85–97%, depending on the nature of the assay. The protein moieties of chimpanzee VLDL and LDL were dominated by proteins of high M r (180000–380000). The predominant component had M r 330 000–380 000, and migrated similarly to the human B100 protein; a second band ( M r = 235 000–285 000) apparently corresponded to the human B74 protein. Fractionation of apo-LDL by gel filtration chromatography in anionic detergent yielded a void volume fraction which we have termed chimpanzee apo-B H . By SDS-gel electrophoresis, apo-B H contained counterparts (bands I and II) to the human B100 and B74 proteins, with the B100-like component (band 1) dominating. The amino acid composition of apo-B H was markedly similar to that of human B100. The structural characteristics of the major molecular form(s) of circulating LDL in chimpanzee are similar to those of the corresponding particles in man, supporting the contention that P. troglodytes is a highly suitable model for studies of the role of LDL and apo-B H in atherogenesis.