Characterization of 1-methyladenine binding in starfish oocyte cortices

M. Yoshikuni, K. Ishikawa, M. Isobe, T. Goto, Y. Nagahama

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Abstract

1-Methyladenine (1MeAde) is the naturally occurring maturation-inducing hormone of starfish oocytes. We have prepared a biologically active [3H]1MeAde of high purity and relatively high specific radioactivity. This ligand binds to cortices isolated from full-grown prophase-arrested oocytes of the starfish Asterina pectinifera. The binding of [3H]1MeAde to cortices was rapid and reached equilibrium in ~15 min. This is in excellent agreement with the hormone-dependent period required for the induction of oocyte maturation. Binding was maximal between pH 6.4 and 8.0 and diminished sharply above and below this range. Analysis of Scatchard plots of the equilibrium binding of [3H]1MeAde to cortices indicates the existence of a single class of binding site with a dissociation constant of 0.3 μM and a binding capacity of 0.02 fmol per cortex. Whereas biologically active analogs (1-benzyladenine, 1-ethyladenine) inhibited the specific binding of [3H]1MeAde by cortices, biologically inactive analogs (2-methyladenine, 3-methyladenine, 1,9-dimethyladenine, and 1-methylhypoxanthine) did not. These results suggest that the 1MeAde binding characterized herein is necessary for the maturational action of 1MeAde on starfish oocytes.

Original languageEnglish
Pages (from-to)1874-1877
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Volume85
Issue number6
DOIs
Publication statusPublished - Dec 1 1988
Externally publishedYes

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