Deglycosylation of Gonadotropins with an Endoglycosidase

A commercially available endoglycosidase (N-glycanase, Genzyme, Boston, Mass.) purified from Flavobacterium meningosepticum with a specificity for cleaving asparagine-linked carbohydrate moieties in glycoproteins was tested on several pituitary and chorionic gonadotropins as substrates. All intact hormones tested were resistant to the action of the enzyme as were all β subunits from the respective gonadotropins. All α subunits, however, were susceptible to the enzyme as evidenced by a decrease in molecular size when examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE). Preparative experiments with ovine luteinizing hormone subunit (oLHα) indicated that only 35-40% of the carbohydrate was removed after N-glycanase treatment, suggesting that perhaps only one of the two carbohydrate moieties was cleavable under the conditions employed. The enzyme-modified subunit (DG-oLHα) was able to recombine with untreated oLHβ. An in vitro steroidogenic bioassay (rat Leydig cell) showed that the recombinant (DG-oLHα-oLHβ) was about 22% as potent as the native oLH, but in a testicular membrane binding assay for LH, it was equal in potency to the native hormone in competing with the radioligand.