BIG AND LITTLE FORMS OF PLAICE VITELLOGENIC AND MATURATIONAL HORMONES

A gonadotropin, which was not absorbed on Con A-Sepharose and therefore either nonglycoprotein in nature or characterized by a low carbohydrate content or lacking in the appropriate sugars requisite for binding to Con A, had been prepared from plaice (Hippoglossoides platessoides) pituitaries. Filtration through Ultrogel and subsequent chromatography on either Bio-Gel or Ultrogel permit the isolation of two forms with molecular weights of 28,000 and 62,000, respectively. Both molecular species were active in stimulating ovarian growth and vitellogenesis as indicated by their ability to elevate the gonadosomatic index, the ovarian uptake of 33PO43- and [3H]leucine, and the incorporation of the radiolabels into the protein and phosphoprotein fractions of the ovary of the hypophysectomized winter flounder (Pseudopleuronectes americanus), but neither exerted any effect on the processes of oocyte maturation and ovulation. Another plaice gonadotropin, which was potent in stimulating the processes of oocyte maturation and ovulation in the hypophysectomized winter flounder and which also existed in two forms with molecular weights of 28,000 and 62,000, could be isolated from the glycoprotein fraction of the pituitary extract with similar chromatographic procedures. The 28,000 MW gonadotropins manifested a strong tendency to undergo aggregation leading to the formation of the 62,000 MW species in buffer containing low concentrations of EDTA. The phenomenon of assocation could be prevented by the inclusion of a high concentration (10 mM) of EDTA in the elution buffer. High concentrations of sodium chloride and dithiothreitol in the buffer appeared to be less effective in minimizing aggregation. The relative magnitudes of the molecular weights and the comparable biological activities of the two forms are indicative of a monomer-dimer relationship. The winter flounder pituitary also secretes hormones similar in chromatographic behavior to those of the plaice. The presence of two distinct types of biological activities in two chromatographically discrete fractions of the Hippoglossoides platessoides pituitary extract, when tested in a closely related species Pseudopleuronectes americanus after hypophysectomy, constitutes the first unequivocal evidence based on both biochemical and physiological criteria for the existence of separate gonadotropins controlling vitellogenesis and maturation in a teleost. © 1978.