Summary: was grown in continuous culture at different dilution rates under either methanol or oxygen limitation. Methanol dehydrogenase and formate oxidation were repressed by the presence of high concentrations of methanol in the growth medium, whereas hexulose phosphate synthase was constitutive and the glucose-6-phosphate and 6-phospho-gluconate dehydrogenases were regulated only by the growth rate. Chemical analysis and C NMR spectroscopy showed that the oxidation of methanol was accompanied by the spillage of 0 to 50% of the input carbon as formaldehyde and dihydroxyacetone, the extent of which reflected the methanol dehydrogenase: hexulose phosphate synthase activity ratio and/or the energy status of the cells. It is concluded that the observed regulation of key enzymes of methanol and formaldehyde metabolism by the growth environment occurs in order to achieve the required rates of energy conservation and carbon flux demanded by the imposed growth rate, and that the spillage of formaldehyde and dihydroxyacetone reflects limitations on metabolism imposed by kinetic and/or metabolite pool effects.


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