Study of regulation of acid excretion from the cells of plaque bacteria

(1)研究了钠离子和钾离子对变形链球菌糖酵解细胞胞内产酸和酸排泄的影响。一种pH敏感的荧光染料，他（羧乙基）-羧荧光素允许连续监测细胞内pH值，而质子排泄与pH-stat同时测量。钠离子抑制和钾离子，在低pH下，加速可测量的酸的细胞外排泄量。在NaCl （0.15 ~ 0.30 M）的作用下，羧酸的总分泌量被抑制了31%。细胞内果糖1,6-二磷酸水平增加了58%，3-磷酸甘油酸和丙酮酸水平分别下降了46%和12%。钠离子存在时，细胞内pH值降低。可能是细胞内的低pH抑制了糖酵解酶的活性，这些酶参与了果糖1,6-二磷酸分解为3-磷酸三酯。在pH 5.5下生长的细胞比在pH 7.0下生长的细胞从葡萄糖中分泌更多的质子和羧酸。酸性培养的细胞保持细胞内pH值高于中性培养的细胞。这些结果表明，当细胞在酸性pH水平下生长时，酸的排泄增加(4)。在严格厌氧条件下，当反应液pH为5.0时，0.025 mM NaF可抑制pH 7.0细胞50%的质子排泄。这样的氟化物水平比以前报道的低10到20倍。研究了不同pH条件下氯己定（0.025mM）单用、氟（0.05 mM ~ 0.4 mM）单用和氯己定-氟联用对糖酵解链球菌细胞质子排泄和胞内pH的抑制作用。氯己定-氟化物组合在酸性和中性pH下均具有抗致酸作用。

(1). The effect of sodium and potassium ions on intracellular acid production and acid excretion by glycolyzing cells of Streptococcus mutans was examined. A pH-sensitive fluorescent dye, bis (carboxyethyl)-carboxyfluorescein allowed for the continuous monitoring of intracellular pH while proton excretion was measured simultaneously with a pH-stat. Sodium ions inhibited and potassium ions, at low pH,accelerated the amount of measurable acid excreted extracellularly.(2). In the presence of NaCl (0.15-0.30 M), the total amount of carboxylic acids excreted was inhibited by up to 31%. The intracellular level of fructose 1,6-bisphosphate increased by 58% and levels of 3- phosphoglycerate and pyruvate decreased by 46 and 12%, respectively. The intracellular pH decreased in the presence of sodium ions. It is possible that the low intracellular pH inhibits the activity of the glycolytic enzymes involved in the breakdown of fructose 1,6-bisphosphate to 3- phosphogycerate.(3). The cells grows at pH 5.5 excreted more protons and carboxylic acids than the cells grown at pH 7.0 from glucose. The acidic grown cells kept the intracellular pH higher than the neutral grown cells. These findings indicated that the excretion of acid increased when the cells were grown at acidic pH levels.(4). Under strictly anaerobic conditions, 0.025 mM NaF inhibited proton excretion by 50% in cells grown at pH 7.0 when the pH of reaction mixture was 5.0. Such levels of fluoride are about 10 to 20 times lower than that reported previously.(5). The inhibitory effect of chlorhexidine (0.025mM) alone, fluoride (0.05 mM to 0.4 mM) alone andc hlorhexidine-fluoride combination on proton excretion and intracellular pH in glycolyzing streptococcal cells were examined under different pH conditions. The chlorhexidine-fluoride combination had the advantage of anti-acidogenic effects at both acidic as well as neutral pH levels.