Functional Groups in Ovine Luteinizing Hormone and Their Receptor Site Interactions

Abstract

Selective chemical reactions have long been used in the field of hormone research for the study of functional group relationships to biological activity. An early example of such a study applied to ovine LH is that of Li, Simpson and Evans (1) who employed ketene to acetylate LH (ICSH) and found that acetylation under very mild conditions inactivated the hormone. Geschwind and Li (2) found periodate oxidation inactivated ovine LH. Although in that study periodate was selected for its attack on vicinal hydroxyl groups in the carbohydrate moiety, these authors appreciated that other reactions might be taking place. In a later study from that same laboratory Gan et al. (3) demonstrated that periodate oxidation of ovine LH not only attacked the carbohydrate moiety but also the disulfide bonds in the molecule. Thus, although periodate oxidation inactivates ovine LH it is not known whether this inactivation results from destruction of the carbohydrate moieties, destruction of the disulfide bonds, or both. Our own laboratory made an extensive study of the effect of several reagents and various conditions upon the activity of ovine LH (4). Included in those studies were some on the effects of oxidation by performic acid which attacks the disulfide bonds and the thioether group of methionine. This reagent completely inactivated ovine LH. We also studied the effect of reduction with sodium and liquid ammonia on the biological activity of the hormone. Although the hormone was virtually inactivated by this treatment, it is difficult to be certain in such an experiment that there was not some reoxidation to the native hormone to account for the small residual activity observed. There are also other technical difficulties in dealing with a hormone in the reduced form at the very dilute concentrations which must be used for bioassay.