Porcine Luteinizing Hormone Isoform(s): Relationship between Their Molecular Structures, and RenotropicVersusGonadotropic Activities*

Abstract

We recently demonstrated the renotropic activity in ovine LH isoform(s). In this study we purified porcine (p) LH isoforms and analyzed their structures and bioactivities. Purified pLH preparation (G-100 fraction 3) was dissociated into alpha- and beta-subunits, followed by isolation with reverse phase HPLC. Six components were isolated and analyzed for their amino acid compositions and amino-terminal amino acid sequences. alpha-Subunits were found to have heterogeneous N-terminal sequences, which started at Phe-1, Gly-4, Phe-6, or Thr-7. This N-terminal heterogeneity and the presence of the initial 6 amino acids has not been reported previously to the best of our knowledge. Moreover, the first 10 residues, Phe-Pro-Asp-Gly-Glu-Phe-Thr-Met-Gln-Gly, were identical with those of the ovine LH alpha subunit. At least 3 different beta-subunits were identified as heterogeneous in their carboxyl-terminal amino acids. The pLH preparation (G-100-fraction 3) was then chromatographed by an isoelectrofocusing (IEF) column. Four IEF fractions were obtained. Their amino acid structures appeared to be identical, as judged by the identical elution profiles on reverse phase HPLC, but their carbohydrate compositions were slightly different, especially in N-acetylgalactosamine in alpha-subunits. Thus, fractionation on IEF depended on the heterogeneity in carbohydrate structures. Each IEF fraction had different potencies in terms of its gonadotropic activity (in vitro) and renotropic activity (in vivo and in vitro). The discrepancy was observed not only between gonadotropic activity and renotropic activity, but also between in vivo and in vitro renotropic activity. This study identified the structural heterogeneity of pLH isoforms and demonstrated their biological heterogeneity. We concluded that the carbohydrate structure of the pLH isoform is important for expressing its biological heterogeneity (gonadotropic and renotropic activity.