Production of the oocyte maturation-inducing substance of starfish by heat treatment of S-adenosylmethionine

1-Methyladenine (1-MeA) has been identified as the oocyte maturation-inducing substance (MIS) in starfish, but little is known about its biosynthesis. This study showed that starfish MIS activity was present in a reactant derived from S-adenosylmethionine (SAM) by heat treatment. In vitro MIS production was markedly dependent on the temperature of the SAM solution: it increased as the temperature was raised, and reached a plateau within 5 min upon boiling, although hardly only MIS was observed upon incubation below 20°C. MIS production was also dependent on the solution pH. Analyses by high-performance liquid chromatography and thin-layer chromatography showed that the MIS was 1-MeA, though the maximum amount of 1-MeA obtained from SAM by boiling was only 0.3% of the initial SAM amount. Furthermore, use of S-[¹⁴C-methyl]SAM showed that a methyl group of 1-MeA was transferred from the SAM. Thus, it is possible that 1-MeA may be produced from SAM in vivo.