Promotion of Streptococcus mutans glucose transport by human whole saliva and parotid fluid.

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RESUMO

Human saliva and parotid fluid have two effects on glucose uptake by Streptococcus mutans: a reduction in the overall rate of uptake, and the promotion of a biphasic mode of uptake. The former effect had been previously shown to result from lactoperoxidase-mediated inhibition of transport or metabolism or both. The objective of the present study was to uncover the basis of the second effect. Biphasic glucose uptake consisted of a rapid phase of low capacity and short duration (approximately 10 to 15 s) followed by a slower phase of high capacity and long duration (several minutes). The slow phase is typical of cells not exposed to the secretions (control cells). S. mutans BHT cells pretreated with as little as 10 microM glucose for 10 min at 37 degrees C, followed by its removal, subsequently exhibit biphasic glucose uptake typical of saliva- or parotid fluid-treated cells. Since pretreatment of the organism with glucose, whole saliva supernatant, or parotid fluid supported subsequent transport of the nonmetabolized glucose analog, 2-deoxyglucose, we concluded that pretreatments established a relatively stable pool of glycolytic intermediates (i.e., a phosphoenolpyruvate potential). Thin-layer chromatographic analysis of extracts from [14C]glucose-pretreated cells confirmed the presence of a stable pool of triose phosphates. Dialysis experiments indicated that high-molecular-weight substrates in the secretions were readily utilized by the organism to establish a phosphoenolpyruvate potential, especially when the lactoperoxidase system was rendered inactive. A survey of several carbohydrate constituents of salivary glycoproteins revealed that mannose, galactose, and N-acetylglucosamine, in addition to glucose, established phosphoenolpyruvate potentials in the organisms. Inactive substances included, among others, N-acetylgalactosamine and N-acetylneuraminic acid. In a survey of selected amino acids, arginine alone promoted 2-deoxyglucose accumulation by the organism, albeit feebly. Finally, it is argued that the phenomenon of biphasic glucose uptake provides evidence that the rate limiting step in glucose uptake by S. mutans is glucose metabolism and not glucose transport.

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