Effect of Disulfide-Reducing Agents on Activity of 1-Methyladenosine Ribohydrolase in Starfish Follicle Cells: (starfish follicle cells/1-MeAde biosynthesis/1-MeAde-Rase/sulfhydryl group).

Abstract

Production of 1-methyladenine (1-MeAde) in isolated starfish follicle cells incubated with 1-methyladenosine was elevated by disulfide-reducing agents, such as dithiothreitol, cysteine, and homocysteine. More than 0.05 mM cysteine and homocysteine brought about a six-fold increase of 1-MeAde production in comparison with controls without disulfide-reducing agents. On the other hand, iodoacetamide, which is a membrane-permeable SH-blocking agent, decreased the 1-methyladenosine-induced 1-MeAde production. A forty percent decrease of 1-MeAde production was obtained with 0.5 mM iodoacetamide. Iodoacetamide inhibited also 1-MeAde production induced by gonad-stimulating substance (GSS). But a membrane-impermeable SH-blocking agent, N-carboxyphenylmaleimide, failed to inhibit both 1-methyladenosine-induced and GSS-induced 1-MeAde production. Furthermore, partially purified 1-methyladenosine ribohydrolase was activated by dithiothreitol, 2-mercaptoethanol, and cysteine derivatives. An approximately ten-fold activation was obtained with these disulfide-reducing agents at concentrations of more than 5 mM. On the contrary, though the SH-blocking agents inhibited 1-methyladenosine ribohydrolase, the inhibition was relieved by the disulfide-reducing agents. These results suggest that the reduced form of SH-group in 1-methyladenosine ribohydrolase plays an important role for enzymatic activation.