Physico-chemical and immunological characteristics of pituitary prolactin from water buffaloes (Bubalus bubalis)

Abstract

Prolactin (PRL) was purified from freshly frozen pituitary glands of water buffaloes (Bubalus bubalis) by a combination of existing procedures of Ellis and Jiang and Wilhelmi involving serial extraction of different pituitary proteins. The partially purified preparation was further fractionated on DEAE-Sephadex followed by Sephadex G-100 chromatography. This was finally purified on HPLC. This preparation was found to be homogeneous by SDS-PAGE and HPLC and had a single N-terminus amino acid (Threonine). The molecular size was estimated to be 24K +/- 0.5 by SDS-PAGE and approximately 25K by GPC-HPLC. The buffalo PRL gave a dose dependent inhibition curve in a rat liver based radio receptor assay with a potency of 30-35 I.U./mg and also in a partial homologous RIA using 125I-buffalo PRL and rabbit anti-oPRL serum giving a potency of 30 I.U./mg. Metabolic labelling studies using 35SO4(2-) with buffalo pituitary minces showed the incorporation of radioactive sulfate into immunoprecipitable PRL-like material. Physico-chemical characterization of the site of the linkage between sulfate and PRL revealed the presence of Tyr-O-SO4 in bu-PRL. A high affinity monoclonal antibody (MAB) with Ka of 10(10) L/M, belonging to IgG1 isotype, and capable of cross reacting with ovine and bovine PRL was generated. This MAB was conformation specific as reduced and carboxymethylated PRL did not react with it. A homologous RIA system using this MAB has been standardised.