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In Saccharomyces cerevisiae the HXK2 gene, which encodes the glycolytic enzyme hexokinase II, is involved in the regulatory mechanism known as ‘glucose repression’. Its deletion leads to fully respiratory growth at high glucose concentrations where the wild type ferments profusely. Here we describe that deletion of the HXK2 gene resulted in a 75% reduction in fermentative capacity. Using regulation analysis we found that the fluxes through most glycolytic and fermentative enzymes were regulated cooperatively by changes in their capacities ( Vmax) and by changes in the way they interacted with the rest of the metabolism. Glucose transport and phosphofructokinase were regulated purely at the metabolic level. The reduction of fermentative capacity in the mutant was accompanied by a remarkable resilience of the remaining capacity to nutrient starvation. After starvation, the fermentative capacity of the hxk2Δ mutant was similar to that of the wild type. Based on our results and previous reports, we suggest an inverse correlation between glucose repression and the resilience of fermentative capacity towards nutrient starvation. Only a limited number of glycolytic enzyme activities changed upon starvation of the hxk2Δ mutant and we discuss to what extent this could explain the stability of the fermentative capacity. [ABSTRACT FROM AUTHOR]

Abstract: A novel method dissecting the regulation of a cellular function into direct metabolic regulation and hierarchical (e.g., gene-expression) regulation is applied to yeast starved for nitrogen or carbon. Upon nitrogen starvation glucose influx is down-regulated hierarchically. Upon carbon starvation it is down-regulated both metabolically and hierarchically. The method is expounded in terms of its implications for diverse types of regulation. It is also fine-tuned for cases where isoenzymes catalyze the flux through a single metabolic step. [Copyright &y& Elsevier]

Examines pathway for the catabolism of branched-chain alpha-keto acids. Identification of a single promoter upstream of the bkd gene cluster; Formation of adenosine triphosphate via substrate level phosphorylation with the conversion of branched-chain alpha-keto acids to free acids; Characteristic active pathway under aerobic and anaerobic conditions.

Examines the extensive regulation for DNA gyrase controls DNA supercoiling and growth rate of Escherichia coli. Modulation on the expression of DNA gyrase; Measurement on the effects for plasmid by readjusting gyrase transcription; Regulation of homeostasis by physiological DNA structure.