Role of Carboxyl Groups in the Secondary Structure and Function of Sturgeon Gonadotropin

Free negatively charged carboxyl groups were selectively modified (neutralised) in sturgeon (Acipenser güldenstädti Br.) gonadotropic hormone (GTH) α and β subunits. Eleven free carboxyl groups, three in the α and eight in the β subunit, were neutralised by reaction with glycine ethyl ester. Investigation of reassociated α-β dimers (recombinants) comprising one or both modified subunits showed that specific hormonal activity was completely lost while immunoreactivity was lowered in comparison with that of the standard α-β dimer. CD-spectroscopy of the modified subunits did not indicate any considerable changes in their spatial structure. A conclusion was made that free COOH groups of GTH were important as bearers of the negative charge necessary for the hormone activity on the level of the hormone-specific membrane receptors.