Study on dynamic change of sugar metabolism by microorganisms in dental plaque due to the drastic change of oral environments.

口腔环境时时有很大变化。因此，牙菌斑中的产酸受到环境变化的影响，而牙菌斑是龋齿发生和发展的必然事件。我们研究了口腔环境可能的变化对链球菌、放线菌和乳杆菌等口腔微生物产酸的影响。在神经酸碱值时，已知链球菌在糖供应有限的情况下，除了乙醇外，还会产生甲酸和醋酸。但在pH值为5.5时，即使糖的供应有限，甚至在严格的厌氧条件下，链球菌也主要产生乳酸。链球菌产乳酸的关键酶-乳酸脱氢酶(LDH)在低pH条件下被诱导，而丙酮酸甲酸裂解酶(PFL)在严格厌氧条件下不被诱导。LDH的最佳PB低于PFL。因此，链球菌细胞中的低pH也被认为是在低pH条件下转变为乳酸发酵的原因。PFL是在厌氧条件下，在可发酵糖的存在下被激活的。对于这种激活，NADPH被发现是一个必不可少的因素。这意味着PFL作为厌氧糖代谢的重要酶，在链球菌的糖代谢过程中受到精细的调控。在内氏放线菌、粘性放线菌中也发现了PFL的存在和类似的调控。乳杆菌病例和乳链球菌。

The environment of oral cavity changes greatly from time to time. Thus acid production In dental plaque, an inevitable event for the initiation and progression of dental caries, is affected by this change of environment. We studied the effect of possible change of oral environment on the acid production of oral microorganisms, such as streptococcal, actinomyces and lactobacilli.The pH in dental plaque drops during meals due to the uptake of sugars. At neural pH streptococci have been known to produce formic andacetic acids in addition to ethanol when supply of sugar is limited. But at pH 5.5 streptococci produced mainly lactate even if supply on sugar is limited and even under strictly anaerobic conditions. The lactate dehydrogenase (LDH), a key enzyme of lactate production , of streptococci was found to be induced at low pH, while pyruvate formate-lyase (PFL), a key enzyme of formic and acetic acids production under strictly anaerobic conditions, was not induced. The optimum PB of the LDH was lower than that of PFL. Thus the low pH in the cells of streptococci was also considered responsible for this change into lactate fermentation at low pH. PFL is activated under anaerobic conditions in the presence of fermentable sugar. For this activation NADPH was found to be an essential factor. This means that the activation PFL, an important enzyme of anaerobic sugar metabolism, is finely regulated during sugar metabolism of streptococci. A presence and a similar regulation of PFL were also found in Actinomyces naeslundii, Actinomyces viscosus. Lactobacillus cases and Streptococcus lactis.