Comparison of biotin binding protein of pregnant rat serum with rat serum albumin

Abstract

The purified biotin-binding protein of pregnant rat serum was immunol. similar to rat serum albumin as assessed by a sensitive RIA. In RIA for rat biotin-binding protein, the binding of [125I] rat biotin-binding protein to anti-chicken egg yolk biotin-binding protein antibodies was displaced by both rat serum (10-100 nL) and purified rat serum albumin (0.1-10 ng). Similarly, in RIA for rat serum albumin the binding of [125I] rat serum albumin to either anti-rat serum albumin antibodies or anti-chicken egg yolk biotin-binding protein antibodies was displaced by unlabeled rat biotin binding protein at comparable concn. (0.5-10 ng). Significant fractions of radioiodinated rat biotin-binding protein and rat serum albumin bound to antibodies to chicken egg yolk biotin-binding protein. In immature rats, the circulating half-lives of rat biotin-binding protein and rat serum albumin were 12 and 17 h, resp. The rat biotin-binding protein and rat serum albumin were analyzed by techniques that exploit their physicochem. properties. They displayed similar electrophoretic mobilities in alk. as well as denaturing SDS-PAGE. However, in nonequil. pH gradient PAGE they resolved clearly. In 2-dimensional tryptic peptide map anal., the 2 proteins showed similarities as well as significant differences in the relative distribution patterns of their iodopeptides. Thus, the primary structure of rat biotin binding protein and rat serum albumin were different in finer details despite the fact that they shared significant immunol. crossreactivity