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Abstract
Bakers’ yeast (Saccharomyces cerevisiae) has been grown in continuous culture using a control medium and media which contained low levels of ammonium and phosphate. The effects of medium composition and growth rate on the levels of intermediates of the glycolytic pathways, the tricarboxylic acid cycle and the glyoxylate cycle were investigated. The energy charge varied only between 0·7 and 0·9 over the range of dilution rates studied; however, the level of ATP decreased by 50% at higher aerobic growth rates. Intermediates of the Embden-Meyerhof-Parnas pathway were higher at the low aerobic growth rates and decreased as the dilution rate was increased. However, higher levels of these intermediates were also observed at even higher dilution rates at which ethanol formation and fermentative metabolism occurred. Significant differences in levels of intermediates were observed between control experiments and fermentations using the low nitrogen and phosphate media. The greatest differences were observed in the levels of glucose 6-phosphate, 6-phosphogluconate, pyruvate, citrate and glyoxylate. Twenty-one different steady states were investigated and each was found to have a unique composition.
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