TRYPTIC MAP VARIATION OF ERYTHROPOIETIN RESULTING FROM CARBOXYPEPTIDASE B-LIKE ACTIVITY

The recombinant human erythropoietin (r-HuEPO) is monitored by tryptic mapping for its purity and identity. Occasionally, these maps have produced an additional peak not evident in the reference standard. This peak was isolated, sequenced and characterized by mass spectrum. it is derived from a known r-HuEPO tryptic peptide 144-150 with the C-terminal arginine removed. Its formation can be reduced or totally eliminated by the addition of inhibitors of carboxypeptidase B activity. These results indicate the presence of residual carboxypeptidase B-like activity in some r-HuEPO lots. Similar enzymatic activity has been shown in varying amounts in the concentrated diafiltered media before purification. The peptide 144-150 is one of the first to be affected by the carboxypeptidase B-like activity. This peptide seems to locate in the most trypsin-sensitive part of r-HuEPO.