Insulin-stimulating peptide from tryptic digest of bovine serum albumin

Insulin-stimulating peptide was isolated from a tryptic digest of bovine serum albumin by gel permeation, SP Sephadex column chromatography, reversed phase HPLC and cation-exchange HPLC. This peptide, with a molecular weight of about 8,400, had no insulin-like activity by itself, but enhanced fatty acid synthesis from glucose in rat adipose tissue explants in the presence of suboptimal concentrations of insulin. It also stimulated the effect of insulin on CO2 production from glucose in rat adipocytes, without affecting insulin binding. These stimulations were dose-dependent and were observed at concentrations of more than 2 X 10(-7) M peptide only in the presence of a suboptimal concentration of insulin.