Highly Acidic Proteins in Bovine Liver1

Abstract

Highly acidic proteins were extracted from bovine liver with 55% saturated ammonium sulfate and purified by DEAE-Sephadex A-50 column chromatography and Sephadex G-75 column chromatography. Four acidic protein fractions (BLA I–IV) were obtained in yields of 150, 100, 50, and 450 mg, respectively, from 6kg of bovine liver. When analyzed by 7.5% and 15% polyacrylamide gel disc electrophoresis, BLA I and BLA II fractions were still heterogeneous, and BLA III fraction was composed of two main and one minor protein components. On the other hand, BLA IV fraction was homogeneous after rechromatography on DEAE-Sephadex A-50. Gel electrophoresis also showed that the four acidic protein fractions were clearly different each other. The molecular weights were estimated to be 12,500 and 14,500 for the two main protein components of BLA III fraction, and 16,000 for BLA IV, as determined by SDS-polyacrylamide gel electrophoresis. Three N-terminal amino acids for BLA III fraction were identified by a dansylation method, but none was found for BLA IV. BLA IV showed an unusual UV spectrum, while BLA I-III fractions gave usual protein spectra. BLA III and BLA IV fractions were compared with highly acidic proteins of bovine brain (PAP I and PAP II). BLA III fraction was different from PAP I (bovine brain S-100 protein) and BLA IV fraction was virtually identical with PAP II, on the basis of amino acid compositions and peptide maps of tryptic digests. Immunodiffusion tests with anti-S-100 serum demonstrated that S-100 protein could not be detected in bovine liver; the content is less than one-thousandth of that in bovine brain. Thus, S-100 protein was not detected in bovine liver by chemical analysis or by immunochemical tests. However, it appears that almost identical acidic proteins are present in bovine liver and brain (BLA IV and PAP II) as well as in chick brain (CBA II).