Studies on the oxygen-impairment of the sugar metabolism of micro-organisms in dental plaque and on the biochemical mechanism of its recovery from the impairment.

牙菌斑中的微生物通过糖发酵产生的酸直接参与龋齿的发生和发展。这些微生物的糖代谢也受到有机体与空气接触的极大影响。在日常生活中，尤其是进餐时，牙菌斑中的环境条件变化很大。因此，我们研究了糖代谢从氧损伤中恢复的生化机制，发现变形链球菌的糖代谢比血链球菌更敏感。糖代谢的低敏感性是S. sanguis是由丙酮酸甲酸裂解酶的两种形式之间的相互转化引起的，而S.变异人不能进行这种相互转化。活性丙酮酸甲酸裂解酶转化为无活性形式的酶（R型）时，完整的细胞厌氧培养无糖。当在严格厌氧条件下有糖时，R型酶在细胞中被重新激活。酶的R型对氧不敏感，而活性酶对氧非常敏感。与氧气的接触将活性酶转化为另一种形式的失活酶，这种失活酶不会被重新激活。完整的S.变形菌没有这样的系统将活性酶转化为R型。这可能是为什么S。变异人对氧气敏感。

The acids generated through the fermentation of sugar by the microorganisms in dental plaque are directly involved in the initiation and progression of dental caries. The sugar metabolism by these microorganisms is also affected greatly by the contact of the organisms to air. The environmental conditions in dental plaque vary greatly during the cycle of the daily life, especially by meals. Thus, we studied the biochemical mechanism of the recovery of the sugar metabolism from the impairment by oxygen.We found that the sugar metabolism of Streptococcus mutans was more sensitive than that of Streptococcus sanguis. The low sensitivity of the sugar metabolism of S. sanguis stems from the interconversion of pyruvate formate-lyase between the two forms of this enzyme, while S. mutans cannot do this interconversion. The active pyruvate formate-lyase converted into an inactive form of the enzyme(R-form) when the intact cells were incubated anaerobically without sugar. The R-form enzyme was reactivated in the cells when sugar was available under strictly anaerobic conditions. The R-form of the enzyme was not sensitive to oxygen, while the active enzyme was extremely sensitive. The contact to oxygen converted the active enzyme into another form of an inactive enzyme that was not reactivated. The intact cells of S. mutans had no such a system to convert an active enzyme into the R-form. This could be a reason why S. mutans is sensitive to oxygen.