Protein phosphorylation during 5-hydroxytryptamine-induced maturation of Spisula oocytes.

Maturation was induced in Spisula oocytes with 5-hydroxytryptamine (5-HT) creatinine sulfate at a final concentration of 5 microM. After 10 and 30 min of treatment, oocytes were homogenized and the cytosolic and particulate fractions were prepared. The fractions were incubated with [gamma-32P]GTP and [gamma-32P]ATP. The phosphorylated proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The radioactivity in the gels was determined by autoradiography. With [gamma-32P]GTP a marked increase in the radiolabeling of proteins with an estimated Mr of 47,000 and 20,000 in the cytosolic and particulate fractions, respectively, was demonstrated with the 5-HT-treated oocytes, whereas no stimulation was demonstrable with the use of [gamma-32P]ATP. A significant increase in GTP-mediated protein phosphorylation occurred within 10 min after 5-HT treatment before the occurrence of germinal vesicle breakdown, suggesting that this post-translation modification of proteins is an early action of the neurotransmitter in the induction of meiotic reinitiation in oocytes.