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

Abstract

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 that 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, fiom cell structural'elemepts. In vitro, G6PDH is associated with the insoluble matrix obtained fiom 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 in culture stimulated by growth factors. The occurrence of this phenomenon in such diverse cell types, in response to different stimuli, suggests that the redistribution of G6PDH between insoluble and soluble locations may be involved in the regulation of the pentose phosphate shunt during cell activation in general.

Developmental arrest: from sea urchins to seeds

“…However, upon fertilization, its localization changed from the insoluble (inactive) to soluble (active) fraction (Isono, 1963;Isono et al, 1963;Ii and Rebhun, 1982;Epel, 1986, 1995). If G6PD was assayed in situ using permeabilized eggs, the enzyme activity increased rapidly following fertilization, as did NADPH levels (Epel, 1989;Rees et al, 1996). These egg experiments suggest the need for refinement of the 'grind and find' approach previously used in seed studies.…”

Reduced nicotinamide adenine dinucleotide phosphate and the higher incidence of pollution‐induced liver cancer in female flounder

“…Although G6PDH is a housekeeping enzyme, cellular activity of G6PDH is highly regulated [65,75]. Nutrition, insulin, glucocorticoids, and estrogens are regulators at the transcriptional level and at the level of stability of the mRNA [65,66,70,76], but activity is also regulated at the posttranslational level by, e.g., growth‐inducing cytokines such as epidermal growth factor [77] and intracellular calcium levels [78,79]. This posttranslational regulation can be exerted by means of binding to structural elements, most likely related with ribosomes attached to the endoplasmic reticulum [80].…”