Physical, biological, and immunological characterization of highly purified urinary human chorionic gonadotropin...

A highly purified urinary hCG preparation was subjected to electrofocusing on polyacrylamide gel. It was shown to fractionate into at least 11 components that can be detected by coomassie blue staining, a radioligand-receptor assay (RRA), and four hCG RIAs using antisera against the purified hCG, its alpha- and beta-subunits, and the hCG beta carboxyl-terminal peptide. Refocusing shows that these components are not artifacts of the electrofocusing technique. Six of the major components were isolated, and their pIs were shown to correlate with their sialic acid content. When these components were assayed by radioligand-radioreceptor assay, the four hCG RIAs, and a rat uterine weight assay, they showed 1) similar in vitro biological activities, 2) identical immunological activities that were indistinguishable from the in vitro biological activities, 3) hCG-like and not hLH-like immunological characteristics, and 4) different in vivo biological activities which increased with sialic acid content. Thus, sialic acid alone and/or differences in subunit assembly seem to be responsible for the electrophoretic heterogeneity of highly purified hCG.