METABOLIC CHANGES DURING SEXUAL DIFFERENTIATION IN ALLOMYCES

Oxygen tension was the primary factor inducing the sexual differentiation of the female colonies of Allomyces. Vegetative colonies, or colonies at successive states of induced sexual differentiation, were submitted to increasing periods of anoxia and analyzed for their content in some key metabolites. 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 fructose diphosphate (FDP) fructose-6-phosphate (F-6-P) ratio was drastically lowered, indicating a shut-off of the phospho-fructokinase (PFK) activity. 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. 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. 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.