Changes in the oxidative metabolism during maturation of amphibian oocytes.

Some aspects of oxidative metabolism during cytoplasmic maturation of the Bufo arenarum oocyte have been studied. During the autumn-winter period (immature oocyte), carbohydrates are degraded through the glycolytic pathway, followed by the classical tricarboxylic acid cycle. During the spring--summer period (mature oocyte), carbohydrates are mainly used through the pentose phosphate cycle, while the tricarboxylic acid cycle operates as the glutamic-aspartic cycle. The oxidative phosphorylation of ADP does not seem to change during oocyte maturation. Although maturation does not alter the absolute values of ATP and citrate in the oocyte, it determines their different compartmentalization, which, through phosphofructokinase, in turn regulates the glycolytic activity of the oocyte. Oxygen uptake decreases by about 40% during maturation, while simultaneously, a marked increment in respiratory stimulation by 2,4-dinitrophenol is observed.