Dworkin M B, Dworkin-Rastl E
Ernst-Boehringer-Institut, Vienna, Austria.
Mol Reprod Dev. 1992 Aug;32(4):354-62. doi: 10.1002/mrd.1080320408.
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 [14C]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.
非洲爪蟾卵含有大量糖原储备，但在卵裂期间这些糖原不会进行糖酵解处理。在体内，由于缺乏丙酮酸激酶活性，糖酵解途径（Embden-Meyerhof途径）受到抑制，乳酸和丙酮酸的含量相对较低。在原肠胚形成前的晚期囊胚期，乳酸水平升高，这表明糖原分解和糖酵解通量开始启动。然而，通过将ADP共注射到受精卵中，可短暂激活显微注射的[14C]葡萄糖-6-磷酸的糖酵解过程，而通过注射ATP酶马铃薯焦磷酸酶可组成性激活该过程，这表明存在糖酵解活性所需的所有酶。丙酮酸激酶和苹果酸酶这两种参与卵裂期间碳代谢或随后糖原分解激活的酶的同工酶谱，在卵期和原肠胚期之间没有变化。这些数据表明，晚期囊胚期糖原分解和糖酵解的激活可能不是新基因活性的结果，而可能是游离ADP增加的代谢后果，游离ADP随后能够支持丙酮酸激酶反应。
