STUDIES ON HUMAN CHORIONIC GONADOTROPHIN

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Abstract
Six preparations of Human Chorionic Gonadotrophin (HCG), differing in purity and biological potency, were analysed for their carbohydrate and amino acid composition. The results of the determinations indicated a certain relation between the biological potency on the one hand, and the content of certain substances, particularly sialic acid and fucose (both carbohydrate terminal groups of glycoproteins), on the other. As the sialic acid fraction contained only N-acetyl-neuraminic acid (NANA), a true quantitative determination could be made. Two methods used for the release of NANA were compared and it was found that neuraminidase from Vibrio cholerae released 96% of the amount of NANA which could be released by 0.01 n hydrochloric acid hydrolysis. Based on the results of biological and NANA assays of 16 preparations, a mathematical relation between the biological potency and the NANA content, as an independent variable, was calculated. Membrane electrophoresis in Veronal-formamide buffer revealed a sharp band pattern, which could be explained by assuming a polymorphous HCG molecule, differing mainly in the number of terminal NANA groups. The prospects of a chemical assay of HCG based on the determination of NANA are, however, not at all encouraging.

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