Metabolic changes during sexual differentiation in Allomyces

Summary

• 1. Oxygen tension was found to be the primary factor inducing the sexual differentiation of the female colonies of Allomyces.

• 2. Vegetative colonies, or colonies at successive stages of induced sexual differentiation, were submitted to increasing periods of anoxia and analyzed for their content in some key metabolites.

• 3. Long periods of aeration altered the balance of the adenylates by favoring the build-up of ATP at the expense of ADP and AMP. During the same time, the FDP/F-6-P ratio was drastically lowered, indicating a shut-off of the PFK activity.

• 4. Anoxia was little effective in altering the balance of the adenylates or hexosephosphates in vegetative colonies. However, differentiating colonies were readily affected by anoxia: the balance of the adenylates shifted rapidly in favor of ADP and AMP, and the ratio between FDP and F-6-P rose markedly, pointing to an increased activity of the PFK.

• 5. From the different sensitivities to anoxia exhibited by ATP in vegetative vs. differentiated colonies, it was concluded that the sexual differentiation is accompanied by a shift of the respiratory pattern from a glycolytic to a predominantly oxidative one. This conclusion was further supported by the decrease of PFK endogenous activity during the differentiation; the ineffectiveness of anoxia in promoting PFK activity in vegetative colonies, contrasting with its ability to increase the FDP/F-6-P ratio in differentiating ones, points to the fact that glycolysis in vegetative colonies proceeds at nearly maximum capacity but substantially decreases during differentiation.

• 6. The concomitant changes undergone by the adenylates and the citrate on one hand, and by the FDP/F-6-P ratio on the other hand, are consistent with a regulation of the PFK activity by feed-back inhibition.