Oxygen sensitive pyruvate formate-lyase and its activating enzyme in oral microorganisms.

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Pyruvate formate-lyase (PFL) is a key enzyme of production of formic and acetic acid and ethanol by streptococci under anaerobic conditions. PFL was converted between oxygen-sensitive, active and oxygen tolerant, inactive forms in the cells of Streptococcus sanguis but not in the cells of Streptococcus mutans. All PFL was kept active in S.mutans cells. The biochmical mechanism of this difference in the interconversion was investigated. NADPH was the most efficient reducing agent for the activation of the inactive PFL of S.mutans. On the contrary, NADPH was not so efficient in S.sanguis. Fe^<2+> and selenium were required for PFL activating enzyme, and protein radial was involved in the active center of PFL.PFL inactivating enzyme, which converted active form to oxygen-tolerant inactive form, was found in streptococci. S.sanguis had higher activity of PFL inactivating enzyme than S.mutans.Intracellular conversion of PFL could be explained by these findings. Minute levels of pyruvate and inorganic phosphate inhibited the activity of PFL inactivating enzyme and kept active form of PFL.However, CoA enhanced PFL inactivation. These regulatory mechanism could be important teleologically. Glucose or sucrose metabolism was inhibited by sorbitol in S.mutans under certain conditions. The incorporation of sorbitol resulted in high NADH/NAD ratio and inhibited streptococcal sugar metabolism, since PFL activity was not enough to keep the oxidation/reduction balance. Sorbitol also inhibited sugar metabolism of microorganisms in dental plaque in situ.