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Glycogen breakdown in cleaving xenopus embryos is limited by ADP
Author(s) -
Dworkin Mark B.,
DworkinRastl Eva
Publication year - 1992
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.1080320408
Subject(s) - biology , glycolysis , pyruvate kinase , glycogen , biochemistry , blastula , xenopus , glycogen synthase , glycogen debranching enzyme , glycogen branching enzyme , enzyme , gastrulation , gene , embryogenesis
Xenopus eggs contain large stores of glycogen, but this glycogen is not glycolytically processed during cleavage. The Embden‐Meyerhof pathway is inhibited by the absence of pyruvate kinase activity in vivo, and lactate and pyruvate are present at relatively low levels. In the late blastula, just preceding gastrulation, lactate levels increase, indicating the onset of glycogen breakdown and glycolytic flux. Glycolysis from microinjected [ 14 C]glucose‐6‐phosphate could be transiently activated, however, by the coinjection of ADP into fertilized eggs, and constitutively activated by the injection of the ATPase potato apyrase, indicating the presence of all enzymes necessary for glycolytic activity. The isozyme profiles of pyruvate kinase and malic enzyme, two enzymes involved in carbon metabolism during cleavage or in the subsequent activation of glycogen breakdown, do not change between the egg and gastrula stages. These data suggest that the activation of glycogen breakdown and glycolysis in the late blastula is probably not a result of new gene activity but may be the metabolic consequence of increased free ADP that is then able to support the pyruvate kinase reaction.