Microsequence of Polypeptide Hormones: Its Usefulness to Monitor the Isolation of Novel Molecules

Abstract

Novel peptides related to the N-terminal portion of proopiomelanocortin (POMC) (Chrétien et al., 1979) have been isolated and characterized from human and porcine pituitary glands. Since the cysteine residues were previously found in other species, either by protein radioactive micro-sequencing or cDNA sequence, to be consistantly at positions 2, 8, 20, and 24, their purification was monitored with amino acid sequences of peptides labeled at their cysteine residues with [¹⁴C]iodoacetamide. This approach gave us, at all important steps of the isolation, clear indications of the presence of the desired peptides up to their final and complete purification. These results strongly suggest that chemical characterization, whenever possible, should be used to monitor the purification of proteins and polypeptides whose biological activity cannot be measured, as is the case for precursor molecules or some of their fragments. They also support a recent suggestion by Julliard et al. (1980) that at least some form of chemical characterization should be added to any purification carried out solely on the basis of the immunologic competence of the peptides sought.