Isolation and characterization of multiple components of basic gonadotropin from bullfrog (Rana catesbeiana) pituitary gland.

Four gonadotropin components were purified from the basic protein fraction of bullfrog pituitary glands. All the components had high potencies not only in the ovulation assay using Xenopus laevis ovaries but also in the competitive binding assay for rat follicle-stimulating hormone (FSH) using Xenopus laevis testis. The isoelectric points of the four components determined by isoelectric focusing were at pH 8.8, 9.0, 9.1, and 9.3, respectively. No appreciable difference in the physical and chemical properties other than isoelectric points was found among the four components. Their Stokes radius estimated by gel filtration was 2.36 nm. This value was appreciably lower than that reported for mammalian luteinizing hormone (LH). On sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, reduced preparations of the four components each showed two bands, indicating a subunit structure similar to that of mammalian gonadotropins. Their mobilities were greater than those of mammalian LH. The molecular weights of subunits estimated by high-speed gel filtration in 6 M guanidine hydrochloride were lower than those of mammalian LH. The amino acid composition of the four basic components of bullfrog gonadotropin was appreciably different from that of mammalian LH.