Abstract

The aim of the study was to illustrate the radio-receptor assay of beetal recombinant caprine growth hormone (rcGH). Tracer (¹²⁵I-rcGH) was prepared by iodinating beetal rcGH with iodine-125 and its biological activity was analyzed by rabbit anti-rcGH antibodies. Liver microsomal membranes of the Bovidae species (caprine, ovine and bovine) were prepared to study the binding properties of beetal rcGH. The tracer binding was dependent on receptor protein concentration, tracer counts, temperature, time of incubation and assay pH. The maximum percentage specific binding of the tracer to the microsomal membrane was 45% in 32 h at 4°C. In cross-reactive study, human GH competed and displaced the ¹²⁵I-rcGH by binding effectively to the cGH receptor. Scatchard analysis of the rcGH binding suggested a single class of binding site to the caprine microsomal membrane with an affinity of 337.1 ± 82.94 × 10⁹ M^-1 and capacity of 57.61 ± 4.23 fmol mg^-1 while rcGH binding affinity and capacity to the ovine and bovine receptor protein showed 365.4 ± 66.82 × 10⁹ M^-1, 57.69 ± 3.23 (fmol mg^-1) and 392.6 ± 56.25 × 10⁹ M^-1, 56.8 ± 2.56 (fmol mg^-1) respectively. This study provides data for beetal rcGH interaction with microsomal membrane that shall be beneficial to study hormone receptor interactions of other Bovidae species.

Key words: Beetal recombinant caprine growth hormone, Bovidae, iodine-125, microsomal membrane, receptor protein.