Increased ornithine decarboxylase activity during meiotic maturation in xenopus laevis oocytes

The activity of ornithine decarboxylase (ornithine carboxylyase E.C. 4.1.1.17) was studied during meiotic maturation induced in vitro by progesterone in follicle cell-free oocytes. Enzyme activity increased 4–6 fold during maturation, preceding germinal vesicle breakdown. The increase in ornithine decarboxylase activity was inhibited by cholera toxin, an agent that blocks meiotic maturation and increases cAMP levels within the cell. It was also prevented by cycloheximide but not by actinomycin D. Treatment of oocytes with D,L-α-difluoromethyl-ornithine, an irreversible inhibitor of ornithine decarboxylase and of putrescine synthesis, effectively abolished enzyme activity without preventing germinal vesicle breakdown. These observations show that the progesterone-induced increase in ornithine decarboxylase activity is not required for completion of meiotic division of the oocyte.