Stimulation of α-glucosidases from fast-growing rhizobia and Agrobacterium tumefaciens by K+, NH+4, and Rb+

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Abstract
Extracts from cultured fast-growing rhizobia and Agrobacterium tumefaciens contain enzymes for hydrolysis of the .alpha.-glucosides maltose, sucrose, and .alpha.,.alpha.-trehalose. The hydrolysis of all three sugars was stimulated by the presence of K+, Rb+, or NH4+. This stimulation varied from less than 2-fold to more than 12-fold, depending on the bacterial species, culture conditions, and experimental conditions, such as type of enzyme, buffer, and ion concentration. Eight other ions tested, including several divalent cations, did not have any stimulatory effect. Other sources of enzyme (Escherichia coli, Saccharomyces cerevisiae, Oryza sativa, porcine kidney, and Medicago sativa and Glycine max nodule cytosol) contained .alpha.-glucosidases that differed in both substrate specificity and pH optima and were not affected by K+, Rb+ or NH4+ ions. Bacteroids from G. max and Phaseolus vulgaris nodules did not have detectable .alpha.-glucosidase activity. Growth of Rhizobium leguminosarum biovar phaseoli USDA 2667 with one of the .alpha.-glucosides as carbon source increased Vm and substrate affinity for all three disaccharidase activities. The pH optimum for all three enzymes activities in R. leguminosarum bv. phaseoli USDA 2667 was 6.6. Stimulation by specific monovalent cations appears to be novel property of .alpha.-glucosidases in the bacterial family Rhizobiaceae.