Studies on the composition of the protein part of triglyceride rich lipoproteins of human serum: isolation of polymorphic forms of beta 2-glycoprotein-I.

Isoelectric focusing (IEF) of the apoproteins of triglyceride rich human serum lipoproteins gives rise to the separation of some 15-20 protein bands. Three of these bands have been isolated in pure form and were characterized as isoelectric species of beta 2-glycoprotein-I (beta 2G-I). To compare the amino acid composition of these polymorphic forms with a representative specimen of beta 2G-I from total serum it was also necessary to apply a novel isolation procedure using Rivanol, perchloric acid and Heparin-Sepharose affinity chromatography. With the possible exception of the Pro content, the three isoforms were chemically and immunochemically identical. The isoelectric points of the polymorphic forms were 5.75, 6.0 and 6.2. Their molecular weight was identical by SDS polyacryl amide gel electrophoresis (54 000 D).