SUMMARY: The rate of carbon dioxide fixation by during vegetative growth in glucose-limited continuous culture at pH 3·5 was 0·036 μmol CO fixed (mg hyphae) h; during conidium production at pH 6·5 it reached a maximum value of 0·29 μmol CO fixed (mg hyphae) h. During growth in phosphate-limited continuous cultures, containing sufficient glucose to suppress conidiation, the rate of CO fixation was 0·045 μmol CO fixed (mg hyphae) h, and did not increase substantially following an increase in pH to 6·5. The internal hyphal pH remained at approximately 6·5 despite changes in the external pH from 3·5 to 6·5. Phosphoenolpyruvate carboxykinase (EC and pyruvate carboxylase (EC activities estimated in hyphal extracts gave a fixation rate approximately three times the rate of CO fixation in glucose-limited and phosphate-limited vegetative continuous cultures at pH 3·5. In conidiating cultures, phosphoenolpyruvate carboxykinase and pyruvate carboxylase activities approximately equalled the highest CO fixation rates Fixed C was distributed amongst all the major cell components, with the highest percentage in the conidial protein fraction.


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