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The effects of progressive removal of sialic acid (desialylation) on the immunological and biological activity of HCG, as measured by radioimmunoassay (RIA), ovarian ascorbic acid depletion assay (OAAD) and ventral prostate weight assay (VPW), have been evaluated. Two highly purified HCG preparations with potencies of about 12,000 IU/mg (bioassay, 2nd Int. Std. HCG) and about 5000 IU/mg (immunoassay, 2nd Int. Std. HCG), were used in these studies. Progressive desialylation was achieved by treating the HCG with varying amounts of Clostridium perfringens neuraminidase. Desialylation did not affect immunological activity. Progressive desialylation up to 25 % reduced biological activity by approximately 75% as measured by OAAD and VPW. Desialylation from 25 to 62% reduced biological activity further, the reduction being much more pronounced when measured by VPW than by OAAD, resulting in a considerable increase in the index of discrimination OAAD /VPW. Desialylation from 62 to 100% did not affect biological activity further, giving preparations with a low but significant biological potency with an index of discrimination OAAD /VPW of around 50. (Endocrinology88: 456, 1971)
Hall et al. (Mon,) studied this question.