1-Methyladenine (1-MeAde), the oocyte maturation-inducing substance of star
fish, is produced by ovarian follicle cells upon stimulation with a gonad-s
timulating substance (GSS) released from radial nerves. It has been reporte
d that a process of methylation is involved in GSS-induced 1-MeAde producti
on by starfish ovarian follicle cells. The present study sought to identify
a possible methyl donor for 1-MeAde biosynthesis in follicle cells of the
starfish Asterina pectinifera. When isolated follicle cells were incubated
with [methyl-C-14]methionine (Met), there was an increase in the level of r
adiolabeled S-adenosylmethionine (SAM). After further incubation with GSS,
the [methyl-14C]SAM level decreased, concomitant with a marked increase in
radiolabeled 1-MeAde production. The amount of [methyl-14C]SAM consumed und
er the influence of GSS was similar to the amount of [methyl-C-14]1-MeAde p
roduced. Therefore, it is concluded that SAM is a methyl donor for 1-MeAde
biosynthesis in starfish ovarian follicle cells. On the other hand, it is l
ikely that the purine molecule of 1-MeAde is not derived from SAM but from
ATP. 3-lsobutyl-1-methylxanthine, a potent inhibitor of cyclic AMP phosphod
iesterase, also caused a reduction in the level of radiolabeled SAM followi
ng 1-MeAde production. This suggests that the methylation process of 1-MeAd
e biosynthesis in starfish ovarian follicle cells upon stimulation with GSS
is mediated by a second messenger, cyclic AMP. (C) 1999 Wiley-Liss, Inc.