van Niel Ed W J, Hofvendahl Karin, Hahn-Hägerdal Bärbel
Department of Applied Microbiology, Lund University, SE-22100 Lund, Sweden.
Appl Environ Microbiol. 2002 Sep;68(9):4350-6. doi: 10.1128/AEM.68.9.4350-4356.2002.
A semidefined medium based on Casamino Acids allowed Lactococcus lactis ATCC 19435 to grow in the presence of oxygen at a slow rate (0.015 h(-1)). Accumulation of H(2)O(2) in the culture prevented a higher growth rate. Addition of asparagine to the medium increased the growth rate, whereby H(2)O(2) accumulated only temporarily during the lag phase. H(2)O(2) is an inhibitor for several glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase being the most sensitive. Strain ATCC 19435 contained NADH oxidase (maximum specific rate under aerobic conditions, 426 nmol of NADH min(-1) mg of protein(-1)), which reduced oxygen to water, whereby superoxide was formed as a by-product. H(2)O(2) originated from the dismutation of superoxide by superoxide dismutase. Although H(2)O(2) was rapidly destroyed under high metabolic fluxes, neither NADH peroxidase nor any other enzymatic H(2)O(2)-reducing activity was detected. However, pyruvate, the end product of glycolysis, reacted nonenzymatically and rapidly with H(2)O(2) and hence was a potential alternative for scavenging of this oxygen metabolite intracellularly. Indeed, intracellular concentrations of up to 93 mM pyruvate were detected in aerobic cultures growing at high rates. It is hypothesized that self-generated pyruvate may serve to protect L. lactis strain ATCC 19435 from H(2)O(2).
一种基于酪蛋白氨基酸的半合成培养基能使乳酸乳球菌ATCC 19435在有氧条件下缓慢生长（0.015 h⁻¹）。培养物中H₂O₂的积累阻碍了更高的生长速率。向培养基中添加天冬酰胺可提高生长速率，在此过程中H₂O₂仅在延滞期暂时积累。H₂O₂是几种糖酵解酶的抑制剂，其中3-磷酸甘油醛脱氢酶最为敏感。ATCC 19435菌株含有NADH氧化酶（有氧条件下的最大比速率为426 nmol NADH min⁻¹ mg蛋白质⁻¹），该酶将氧气还原为水，同时产生超氧化物作为副产物。H₂O₂源自超氧化物歧化酶催化超氧化物的歧化反应。尽管在高代谢通量下H₂O₂会迅速被分解，但未检测到NADH过氧化物酶或任何其他酶促H₂O₂还原活性。然而，糖酵解的终产物丙酮酸能与H₂O₂发生非酶促快速反应，因此是细胞内清除这种氧代谢物的潜在替代物。事实上，在高速生长的好氧培养物中检测到细胞内丙酮酸浓度高达93 mM。据推测，自身产生的丙酮酸可能有助于保护乳酸乳球菌ATCC 19435免受H₂O₂的影响。
