POLYAMINE-CONJUGATED PEPTIDE ISOLATED FROM HUMAN-PLASMA

When human plasma was fractionated by gel exclusion chromatography on Bio-Gel P-10, substantial quantities of putrescine and trace amounts of spermidine were consistently associated with a 4200 Mr peptide species. Putrescine was not removed from the peptide by extensive dialysis, desalting, multiple gel and ion exchange chromatographic procedures, nor by incubation with urea followed by trichloroacetic acid precipitation. No putrescine was detected unless the peptide was acid hydrolyzed. Incubation of plasma with 14C-labeled putrescine did not result in association of the label with the peptide. We conclude that these polyamines appear to be covalently bound to this major plasma peptide species. The amount of putrescine associated with the peptide is 10- to 40-fold the concentration of unbound plasma putrescine per equivalent amount of plasma. The peptide was purified to apparent homogeneity and was found to be a single chain composed of 32 amino acid residues with a combined molecular weight of 4180. Possible biological roles of this polyamine conjugated peptide are discussed. © 1979.