Human hypoxanthine-guanine phosphoribosyltransferase. Tryptic peptides and post-translational modification of the erythrocyte enzyme.

This is the authors' abstract. We don't add key points for this paper.

We describe the isolation and characterization of tryptic peptides of human erythrocyte hypoxanthine-guanine phosphoribosyltransferase. The digest was separated by reverse-phase high pressure liquid chromatography into 30 peaks, 26 of which contained purified peptides. The four complex peaks were resolved by high pressure liquid chromatography with a different reverse-phase column. Each peptide predicted from the recently described amino acid sequence of human erythrocyte hypoxanthine-guanine phosphoribosyltransferase was isolated from this peptide map. Sequence analysis of the purified peptides identified two peptides, 14 and 14d, that differed by an Asn/Asp heterogeneity at the position corresponding to residue 106 of the intact protein. Additional studies indicate that this heterogeneity is due to deamidation of the protein in vivo. This post-translational modification appears to be responsible for some of the electrophoretic heterogeneity observed in the normal erythrocyte enzyme.