Isolation and characterization of different molecular and chromatographic forms of heparin-binding growth factor 1 from bovine brain

Bovine brain heparin-binding growth factor 1 (HBGF-1), a single polypeptide (Mr 17,400) with an amino-terminal acetylalanine and three cysteines within the sequence, isolates in multiple truncated and chromatographic forms. The relative yields of the various forms of HBGF-1 depend upon the methods used for purification. Extraction of brain tissue at neutral pH in the presence of protease inhibitors yielded intact acetylala-HBGF-1 and Asn21-HBGF-1 in a ratio of 2.3 to 1. Omission of the protease inhibitors during extraction markedly reduced the yield of acetylala-HBGF-1 and generated predominantly a mixture of Asn21-HBGF-1 and Phe15-HBGF-1. Acetylala-HBGF-1 and Asn21-HBGF-1 can be separated by cation-exchange chromatography prior to further purification. Isolated acetylala-HBGF-1 and Asn21-HBGF-1 distributed into three chromatographic peaks each on reverse-phase high-performance chromatography. Reduction of samples with dithiothreitol prior to reverse-phase chromatography reduced the three peaks of each molecular species into a single peak. Exposure of a single chromatographic peak of HBGF-1 to pH 8 in the absence of a reducing agent generated two or more additional chromatographic peaks upon subsequent chromatography. Although each chromatographic form of different molecular species of HBGF-1 exhibited potent mitogenic activity, reduction of HBGF-1 forms prior to reverse-phase chromatography appeared to increase the specific mitogenic activity of both purified molecular forms.