Regulation of the pentose phosphate pathway at fertilization in sea urchin eggs

Abstract

Summary After fertilization of sea urchin eggs, there is a rapid increase in cellular levels of NADPH, a metabolite utilized in a variety of biosynthetic reactions during early development. Recent studies have shown that a dramatic increase in the activity of the pentose phosphate shunt occurs in vivo shortly after fertilization, consistent with the hypothesis mat this metabolic pathway is a major supplier of NADPH in sea urchin zygotes. One mechanism that may account, in part, for this increase in pentose shunt activity is the dissociation of glucose-6-phosphate dehydrogenase (G6PDH), the first enzyme of the shunt, from cell structural elements. In vitro, G6PDH is associated with the insoluble matrix obtained from homogenates of unfertilized eggs, and in this state, the enzyme is inhibited. Within minutes of fertilization, G6PDH is released as an active, soluble enzyme. A similar solubilization and activation of G6PDH occurs after fertilization of eggs of other marine invertebrates and in mammalian cells...