Studies on the effect of oxygensensitive enzymes on ecology and acid production of dental plaque.

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Ribonucleoside triphosphate reductase is an only one enzyme that catalyzes the reaction to synthesize deoxyribonucleotides in anaerobic microorganisms. This enzyme is an essential enzyme for growth and survival of these microorganisms, because deoxyribonucleotides are material for DNA synthesis. The activity of this enzyme has been measured with radio isotopes. However, the accurate measurement of the activity was diffcult, because this enzyme is extremely oxygen-sensitive and usage of radioisotopes in an anaerobic glove box is legally difficult especially in Japan. We could first develop a method to estimate the activity of this enzyme by photometric method with diphenylamine as a color producing reagent in the cell-free extracts of Escherichia coli. With this method we then find the activity of this enzyme in an oral microorganism, Streptococcus mutans, a strong cariogenic bacterium. To estimate the activity more accurately, we uesd high performance liquid chromatography. Then, we found that the enzyme in S.mutans is also highly oxygen-sensitive and that this enzyme has a reversible inactive form. The inactive form of this enzyme was activated by a similar way as found in another highly oxygen-sensitive enzyme, pyruvate formate-lyase. It is possible that the same activating enzyme activates these two oxygen-sensitive enzymes. These findings sugggest that the variable oxygen concentration in dental plaque affects strongly the activities of these enzymes and then the microorganisms involved in the initiation and development of dental caries as well as periodontal diseases.