Partial purification of rat and human serum factors inhibiting the G1-S transition in rat hepatocytes.

A low molecular weight compound, which inhibits the G1-S transition in rat hepatocytes, was purified from rat trypsin-treated serum by DEAE-cellulose chromatography and high-performance liquid chromatography on three different stationary phases. This procedure led to a 34500-fold purification with a 29% yield. Inactivation of the purified material by specific enzymes showed that the inhibitor is a glycopeptide containing a peptide moiety, N-acetylneuraminic acid and galactose residues. Amino acid analyses indicated the possible existence of a pentapeptide structure. The same purification procedure was applied to the corresponding human inhibitor. Inactivation by specific enzymes showed that it is also a glycopeptide.

Purification and partial characterization of a hepatocyte antiproliferative glycopeptide.

A low molecular weight compound, which inhibits the G1-S transition in rat hepatocytes, was obtained by tryptic hydrolysis of human alpha 2-macroglobulin followed by ultrafiltration at pH 10. It was purified by high-performance liquid chromatography on mu Bondapak C18 and mu Bondapak NH2 with a practically quantitative yield; from 5.1 g of alpha 2-macroglobulin, 2.8 micrograms of purified compound were recovered. Inactivation by specific enzymes and chemical analyses showed that the inhibitor is a sialylated glycopeptide whose peptide moiety contains a pyroglutamyl residue. Its molecular mass, estimated by gel permeation chromatography, would be in the interval 3,500-4,600. However, amino acid analyses indicated that it is not yet pure. All these data suggest that alpha 2-macroglobulin could be the carrier of the precursor form of the glycopeptide.