Difference in the xylitol sensitivity of acidproduction among Streptococcus mutans strains,and its biochemical mechanism

摘要

Although xylitol inhibits the glycolysis of Streptococcus mutans, the degree of inhibition is known to vary among strains. Thus, we studied the biochemical mechanism by which the inhibition varies, using three strains of S. mutans characterized as highly sensitive, moderately sensitive, and resistant to xylitol. The inhibitory effect of xylitol was investigated by measurement of the acid production rate, the metabolic intermediates and the activities of phosphoenolpyruvate phosphotransferase system (PEP-PTS). The results indicate that the higher xylitol: PEP-PTS activity the strain had and the more effectively xylitol inhibited its glucose: PEP-PTS activity, the more sensitive to xylitol the strain was. These observations suggest the following inhibitory mechanisms: (1) direct inhibition of glycolytic enzymes by intracellular accumulation of xylitol 5-phosphate derived from xylitol: PEP-PTS and (2) indirect inhibition through competition for a phosphoryl donor between glucose: and xylitol: PEP-PTS.