NCIB 6346 utilized glucose in preference to maltose when both sugars were present in the growth medium. Addition of glucose to a culture growing on maltose resulted in inhibition of maltose uptake and an immediate cessation of maltose metabolism. The mechanism of maltose transport was examined in whole cells and cell extracts. Phosphoenolpyruvate did not stimulate phosphorylation of maltose, indicating the absence of a phosphotransferase system. However, the presence of a maltose phosphorylase enzyme was suggested by phosphorylation of the sugar in the presence of inorganic phosphate. Maltose accumulation was strongly inhibited by proton conducting uncouplers, and was driven by an artificial transmembrane pH gradient, inside alkaline. These results imply that maltose is transported by a proton symport mechanism in this bacterium.


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