Seki Masanori, Iida Ken-ichiro, Saito Mitsumasa, Nakayama Hiroaki, Yoshida Shin-ichi
Department of Bacteriology, Faculty of Medical Sciences, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan.
J Bacteriol. 2004 Apr;186(7):2046-51. doi: 10.1128/JB.186.7.2046-2051.2004.
Streptococcus pyogenes strains can be divided into two classes, one capable and the other incapable of producing H2O2 (M. Saito, S. Ohga, M. Endoh, H. Nakayama, Y. Mizunoe, T. Hara, and S. Yoshida, Microbiology 147:2469-2477, 2001). In the present study, this dichotomy was shown to parallel the presence or absence of H2O2-producing lactate oxidase activity in permeabilized cells. Both lactate oxidase activity and H2O2 production under aerobic conditions were detectable only after glucose in the medium was exhausted. Thus, the glucose-repressible lactate oxidase is likely responsible for H2O2 production in S. pyogenes. Of the other two potential H2O2-producing enzymes of this bacterium, NADH and alpha-glycerophosphate oxidase, only the former exhibited low but significant activity in either class of strains. This activity was independent of the growth phase, suggesting that the protein may serve in vivo as a subunit of the H2O2-scavenging enzyme NAD(P)H-linked alkylhydroperoxide reductase. The activity of lactate oxidase was associated with the membrane while that of NADH oxidase was in the soluble fraction, findings consistent with their respective physiological roles, i.e., the production and scavenging of H2O2. Analyses of fermentation end products revealed that the concentration of lactate initially increased with time and decreased on glucose exhaustion, while that of acetate increased during the culture. These results suggest that the lactate oxidase activity of H2O2-producing cells oxidizes lactate to pyruvate, which is in turn converted to acetate. This latter process proceeds presumably via acetyl coenzyme A and acetyl phosphate with formation of extra ATP.
化脓性链球菌菌株可分为两类，一类能够产生H2O2，另一类则不能（M. 斋藤、S. 大贺、M. 远藤、H. 中山、Y. 水江、T. 原田和S. 吉田，《微生物学》147:2469 - 2477，2001年）。在本研究中，这种二分法被证明与透化细胞中产生H2O2的乳酸氧化酶活性的有无平行。只有在培养基中的葡萄糖耗尽后，才能检测到有氧条件下的乳酸氧化酶活性和H2O2产生。因此，葡萄糖可阻遏的乳酸氧化酶可能是化脓性链球菌中H2O2产生的原因。在该细菌的另外两种潜在的产生H2O2的酶，即NADH和α - 甘油磷酸氧化酶中，只有前者在两类菌株中均表现出低但显著的活性。这种活性与生长阶段无关，表明该蛋白在体内可能作为H2O2清除酶NAD(P)H连接的烷基过氧化氢还原酶的一个亚基发挥作用。乳酸氧化酶的活性与膜相关，而NADH氧化酶的活性存在于可溶性部分，这些发现与它们各自的生理作用一致，即H2O2的产生和清除。发酵终产物分析表明，乳酸浓度最初随时间增加，在葡萄糖耗尽时降低，而乙酸浓度在培养过程中增加。这些结果表明，产生H2O2的细胞的乳酸氧化酶活性将乳酸氧化为丙酮酸，丙酮酸进而转化为乙酸。后一过程可能通过乙酰辅酶A和乙酰磷酸进行，并形成额外的ATP。
