1-Methyladenosine ribohydrolase in the starfish ovary and its relation to oocyte maturation

Abstract

Maturation of isolated oocytes was induced in the supernatant of an incubation mixture consisting of ovarian fragments, or their extract, and sea water containing 1-methyladenosine in the starfishes, Patiria miniata, Asterias amurensis, Asterina pectinifera. Such maturation-inducing activity was ascribed to the production of an active substance derived from 1-methyladenosine by the action of an enzyme present in ovarian tissue. With column chromatography and thin layer chromatography, the active substance was identified as 1-methyladenine. The enzyme does not seem to be an ordinary adenosine ribohydrolase, but a new specific enzyme to be called 1-methyladenosine ribohydrolase, which splits 1-methyladenosine into 1-methyladenine and ribose. This enzyme was successfully precipitated from the supernatant of ovarian wall homogenate by adding ammonium sulfate at 0.45 saturation. The optimal pH of the enzyme was found to be about 7.5. Its molecular weight was estimated as 96 000 and its isoelectric point was determined as pH 5.1. Ripe ovaries containing fullgrown oocytes showed higher 1-methyladenosine ribohydrolase activity than that of young ovaries, suggesting that the enzyme activity is dependent on the ripeness of the gonad and that the enzyme is related to both oocyte maturation and spawning in starfishes through its ability to produce 1-methyladenine. A gonad-stimulating hormonal peptide, which induces the production of 1-methyladenine in starfish ovaries, had no effect on the activity of 1-methyladenosine ribohydrolase. This suggests that the gonad-stimulating substance acts in some earlier stage of 1-methyladenine biosynthesis.