STUDIES ON A MONKEY PLACENTAL PROTEIN WITH IMMUNOCHEMICAL SIMILARITY TO HUMAN GROWTH HORMONE AND HUMAN CHORIONIC SOMATOMAMMOTROPHIN

ABSTRACT The properties of a monkey placental protein (monkey chorionic somatomammotrophin; MCS) which reacts with antisera directed against human growth hormone (HGH) and human chorionic somatomammotrophin (HCS) have been studied. Following application of monkey placental extracts to Sephadex G-100 and elution with 0.1 m NH4HCO3, two peaks of MCS, with molecular weights of approximately 25 000 and 50 000 were obtained. The electrophoretic mobility of MCS in acrylamide at pH 8.2–8.4 was similar to but less anodal than that of HGH or HCS. The results of immunoelectrophoretic and Ouchterlony double-diffusion studies indicated that MCS is physicochemically and immunochemically distinguishable from HGH and HCS. When tested in a radioimmunoassay for HGH, MCS gave dilution curves intermediate between those for HGH and HCS. In contrast, MCS and HGH gave similar curves in a radioimmunoassay for HCS. MCS, HCS and HGH had very similar effects on the reactions between 131I-HGH and anti-HCS or 131I-HCS and anti-HGH serum. Radioimmunoassay systems for HCS were unsuitable for estimating MCS; however, the above mentioned hybrid assay systems provide a means for approximate quantitation of MCS.