Fordyce A M, Crow V L, Thomas T D
Appl Environ Microbiol. 1984 Aug;48(2):332-7. doi: 10.1128/aem.48.2.332-337.1984.
Nongrowing cells of Streptococcus lactis in a pH-stat were dosed with sugar to allow fermentation at the maximum rate or were fed a continuous supply of sugar at rates less than the maximum. Under anaerobic conditions, rapid fermentation of either glucose or lactose was essentially homolactic. However, with strain ML3, limiting the fermentation rate diverted approximately half of the pyruvate to formate, acetate, and ethanol. At limiting glucose fermentation rates, cells contained lower concentrations of lactate dehydrogenase activator (fructose 1,6-diphosphate) and pyruvate formate-lyase inhibitors (triose phosphates). As a result, pyruvate formate-lyase and pyruvate dehydrogenase play a greater role in pyruvate metabolism. In contrast to strain ML3, strain ML8 did not give the same diversion of products under anaerobic conditions, and cells retained higher concentrations of the above effector compounds. Lactose metabolism under aerobic conditions resulted in pyruvate excretion by both S. lactis ML3 and ML8. At 7% of the maximum utilization rate, pyruvate accounted for 69 and 35% of the lactose metabolized by ML3 and ML8, respectively. Acetate was also a major product, especially with ML8. The data suggest that NADH oxidase is involved in coenzyme recycling in the presence of oxygen and that pyruvate formate-lyase is inactivated, but the pyruvate dehydrogenase complex still functions.
在恒pH条件下，向乳酸链球菌的非生长细胞中添加糖类以使其以最大速率发酵，或者以低于最大速率的速度持续供应糖类。在厌氧条件下，葡萄糖或乳糖的快速发酵基本上是同型乳酸发酵。然而，对于菌株ML3，限制发酵速率会使大约一半的丙酮酸转化为甲酸、乙酸和乙醇。在限制葡萄糖发酵速率时，细胞中乳酸脱氢酶激活剂（果糖1,6 - 二磷酸）和丙酮酸甲酸裂解酶抑制剂（磷酸丙糖）的浓度较低。因此，丙酮酸甲酸裂解酶和丙酮酸脱氢酶在丙酮酸代谢中发挥更大作用。与菌株ML3不同，菌株ML8在厌氧条件下不会产生相同的产物转化，并且细胞中上述效应化合物的浓度较高。在有氧条件下，乳酸链球菌ML3和ML8的乳糖代谢都会导致丙酮酸的排泄。在最大利用率的7%时，丙酮酸分别占ML3和ML8代谢乳糖的69%和35%。乙酸也是主要产物，尤其是对于ML8。数据表明，NADH氧化酶在有氧存在时参与辅酶循环，丙酮酸甲酸裂解酶失活，但丙酮酸脱氢酶复合体仍起作用。
