Effect of amino group modification of ovine luteinizing hormone (oLH) by N-succinimidyl 6-[3-(2-pyridyldithio)propionate]hexanoate, a long chain N-succinimidyl-3-(2-pyridyldithio) propionate (SPDP) on immunological and biological properties: a comparative study with SPDP modified oLH.

The epsilon-NH2 groups of ovine luteinizing hormone has been modified with the long chain N-succinimidyl-3-(2-pyridyl dithiopropionate (LC-SPDP). The LC-SPDP modification primarily occurs in -NH2 groups of the alpha-subunit. Although, the sequential modification of lysine residue in alpha-subunit led to progressive reduction in the receptor binding and immunological properties but the steroidogenic activity was relatively unaffected. The immunoreactivity and receptor binding properties of LC-SPDP modified oLH molecule were more affected comparative to SPDP modified derivatives. This suggested that the increase in hydrophobic carbon chain in LC-SPDP-oLH molecules resulted into the drastic inhibition in the immunological and biological properties. However, the steroidogenic potential of LC-SPDP/or SPDP-oLH derivative was comparable. The present study clearly demonstrate that a single -NH2 group modification with LC-SPDP would generate the site for the conjugation to the toxin/carrier proteins and the resultant oLH-S-S-toxin conjugate would retain significant immunological and biological properties of the hormone molecule.