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Abstract
Mutants of the obligatory aerobic yeast Rhodotorula glutinis were selected after treatment of wild-type cells with N-methyl-N′-nitro-N-nitrosoguanidine on glycerol/glutamic acid medium containing 1%2-deoxy-d-glucose. Rates of d-glucose transport in the mutants were about one-tenth that of the wild-type, whereas the transport of d-fructose and d-xylose was unaffected. However, glucose transport in the mutants was inhibited by uncouplers (for example carbonyl cyanide m-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 2.7.1.2) activity in M8. Thus, the phosphorylation capacity was reduced to one-tenth to one-fifteenth that of the wild-type, resulting in accumulation of d-glucose which, in turn, slowed down net glucose uptake. With the help of the mutant, the stoicheiometry of the H+/glucose symport in R. glutinis was determined to be one proton per molecule of d-glucose transported.
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