THE INVOLVEMENT OF MITOCHONDRIA IN CARBON METABOLISM IN CLEAVING XENOPUS EMBRYOS

The major carbon sources in Xenopus oocytes and cleavage-stage embryos appear to be amino acids, which are oxidized to form pyruvate (to support the Krebs cycle) and phosphoenolpyruvate (for anabolic processes). Metabolism of various metabolites in vitro into aspartate or glutamate, and then partially into phosphoenolpyruvate, requires the presence of mitochondria, suggesting that metabolism in vivo utilizes mitochondrial enzymes. The rate limiting step in metabolism in the stage VI oocyte appears to be uptake and/or metabolism of compounds by the mitochondria; the rate of metabolism increases during maturation. During early cleavage no qualitative differences in metabolism were observed either as a function of development, or spatially along the animal/vegetal or prospective dorsal/ventral axes.