SUMMARY: Mutants of the obligatory aerobic yeast were selected after treatment of wild-type cells with -methyl-'-nitro--nitrosoguanidine on glycerol/glutamic acid medium containing 1% 2-deoxy--glucose. Rates of -glucose transport in the mutants were about one-tenth that of the wild-type, whereas the transport of -fructose and -xylose was unaffected. However, glucose transport in the mutants was inhibited by uncouplers (for example carbonyl cyanide -chlorophenylhydrazone) and, therefore, remained an energy-dependent process. One of the mutants, M8. was chosen for further characterization of the transport and metabolism of hexoses. Biochemical analysis of the hexose-ATP-kinase activities revealed the absence of glucokinase (EC activity in M8. Thus, the phosphorylation capacity was reduced to one-tenth to one-fifteenth that of the wild-type, resulting in accumulation of -glucose which, in turn, slowed down net glucose uptake. With the help of the mutant, the stoicheiometry of the H/glucose symport in was determined to be one proton per molecule of -glucose transported.


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