Physiological differentiation of the mitochondria during Bufo bufo development

1) The oxygen consumption increases during Bufo bufo development in accorda nce with the two steps which border at the "heart beat" stage 2) Cytochrome c oxidase activity is not proportional to the oxygen consumption: it is no table and constant in the first step, and it only increases in the second 3 ) In the mitochondria of preneural embryos, citrate synthase, NADP(+) depen dent isocitrate dehydrogenase, and succinate dehydrogenase activities are v ery low in respect to malate dehydrogenase and glutamate oxaloacetate trans aminase activities. The Krebs cycle results lowered at the condensing react ion level with acetyl accumulation when pyruvate is available. The same beh avior has been observed in the Xenopus laevis oocytes and differentiated ti ssues. 4) The presence of a phosphagen system which is different from creat ine phosphate and arginine phosphate, supporting ATP level, has been demons trated in B. bufo embryos. 5) Mitochondria of portneural embryos are able t o accomplish a complete Krebs cycle by increasing citrate synthase, and suc cinate dehydrogenase activities. 6) In all B. bufo development malate dehyd rogenase and glutamate oxaloacetate transaminase constitute a multienzymati c system by which the mitochondria accomplish a decarboxylic amino acid shu nt required for the transformation of deutoplasm into protoplasm. This shun t is also operative in the X. laevis oocytes. 7) Through pyruvate productio n, by oxidative decarboxylation of malate, the NAD(P)(+) dependent malic en zyme could carry out a fundamental anaplerotic function in the mitochondria which is specialized in the production of biosynthetic blocks belonging to the embryo in which the carbohydrates metabolism rather than the glycolyti c activity is designed for pentose phosphate and glycerol phosphate synthes is for protein and cytomembrane production. 8) Consistent metabolic differe nces have been highlighted between B. bufo embryos and X. laevis embryos.