Factors responsible for glycogenolysis acceleration in early embryogensis of teleosts

An acceleration of the rate of glycogenolysis in the early embryogenesis of the loach (Misgurnus fossilis L.) is accompanied by an increase of the content of hexose monophosphates, the rate of lactate formation and the rate of respiration. The unfertilized egg and the intact embryo of the loach have an identical activity of phosphorylase (EC 2.4.1.1.) and a constant ratio of the active/latent phosphorylase.Following the stage of 32 blastomeres, an increase of phosphorylase activity and the glycogen content occurs in the yolk-free embryo (blastoderm); this increase stops after the onset of gastrulation. In view of the facts that a) the blastoderm contains practically no latent phosphorylase, b) an elevation of phosphorylase activity is synchronized with an increase of the glycogen content, and c) this process is not related to an increase of the total phosphorylase activity and glycogen content in the intact egg, the authors suggest that glycogen-bound phosphorylase transfers from the yolk to the embryo at the stages of cleavage and blastula.In the loach oocyte, unfertilized egg and embryo the main activity of phosphorylase (more than 3/4) is associated with low molecular weight glycogen; this form of glycogen cannot be sedimented at 144000 g, and constitutes not more than 30 % of the total glycogen.Glycogen synthetase (EC 2.4.1.11) is, on the contrary, bound completely with granular glycogen. The oocyte maturation, ovulation and the onset of glycogenolysis after fertilization do not involve a redistribution of enzymes between glycogen fractions of different molecular weights.An increase of the glucose level in oocytes accelerates the conversion of active phosphorylase into its latent form. Physiological concentrations of glucose (up to 2 × 10^-2 M) do not inhibit phosphorylase activity.