Guanidination of ovine luteinizing hormone and effects on activity

Abstract

The free amino groups in oLH, oLHalpha and oLHbeta were guanidinated by O-methylisourea. The epsilon-NH2 groups of lysine residues reacted bo substitute these positions in the sequence with the more basic homoarginine residue. The alpha-NH2 groups did not react under the conditions used. Guanidinated oLH or the products of guanidinated oLHalpha + native oLHbeta or guanidinated oLHalpha + guanidinated oLHbeta were inactive in two bioassay systems. Native oLHalpha + guanidinated oLHbeta, however, showed potencies of 39% to 55% of that observed with the native subunit recombinant or native oLH. Possible structural implications for hormone-receptor site interactions are discussed.

PIP: Data on the guanidination of ovine luteinizing hormone (oLH) and its subunits and the effect of guanidination on subunit-subunit interaction, receptor site binding, and biological activity are presented. Free amino groups oLH, oLH alpha, and oLH beta were guanidinated by 0-methylisourea. The epsilon amino groups of lysine residues reacted to substitute these positions in the sequence with the more basic homoarginine residue. The alpha amino groups did not react. In 2 of the bioassay systems guanidinated oLH or the products of guanidinated oLH alpha plus native oLH beta or guanidinated oLH alpha plus guanidinated oLH beta were inactive. However, native oLH alpha plus guanidinated oLH beta showed potencies of 39-55% of that observed with the native subunit recombinant or native oLH. Possible structural implications for hormone-receptor site interactions are considered.