Effect of magnesium ions on fermentative and respirative functions in Pichia stipitis under oxygen-restricted growth

Mg2+ level affected growth, xylitol and ethanol production by P. stipitis grown under microaerophilic conditions. Low Mg2+ level (1 mM) directed the C flux from ethanol to xylitol, with no effect on xylose consumption rate. The addition of pyrazole, an alcohol dehydrogenase (ADH) inhibitor, had the same effect, even in conditions of Mg2+ excess (4 mM), indicating a negative interaction between ADH and Mg2+ ions (p < 0.01). Cells grown either with pyrazole or Mg limitation increased their intracellular NADH concentration about 3 times, but displayed no significant differences in ADH specific activities (1,000 U/mg protein, +/- 10%). In contrast, no interaction was measured between Mg and antimycin A, excluding the possibility that Mg2+ limitation interferes with respiration.