Presence of nicked components in highly purified preparations of human chorionic somatomammotropin HCS

When purified preparations of human chorionic somatomammotropin (HCS) were examined by polyacrylamide electrophoresis in the presence of mercaptoethanol, four new fast-moving bands were observed, in comparison with the pattern obtained in the absence of the reducing agent. We have found that the new bands correspond to fragments due to the presence of two broken bonds inside the main loop of the HCS chain, and one of these breakage points has been located at Leu 100. It has also been shown that the nicked form corresponds to the slow-moving band in the electrophoretic pattern, obtained in the absence of mercaptoethanol. The nicked form of HCS can be attributed to artefacts during the preparation or to metabolic events. Comparison with HCS prepared by affinity chromatography from retroplacental blood seems to indicate that the former hypothesis is correct.