Imlay J A, Fridovich I
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710.
J Biol Chem. 1991 Apr 15;266(11):6957-65.
Superoxide production has been measured in subcellular fractions of SOD-deficient Escherichia coli provided with physiological reductants. Although cytosolic enzyme(s) do generate O2-., the larger portion is produced by autoxidation of components of the respiratory electron-transport chain. At 37 degrees C and with pO2, NADH, and NAD+ levels matching those in vivo, respiring membrane vesicles generate 3 O2-./10,000 electrons transferred. This corresponds to intracellular O2-. production, in glucose-fed cells, of 5 microM/s. The high SOD content of normal cells restricts O2-. accumulation to 2.10(-10) M, with a moderate gradient from the membrane to the center of the cell. SOD-deficient mutants achieve a much higher steady-state content of O2-.. Rates of superoxide-mediated inactivation of certain enzymes are sufficiently rapid that even 10(-10) M O2-. imposes a significant oxidative stress.
在提供了生理还原剂的超氧化物歧化酶（SOD）缺陷型大肠杆菌的亚细胞组分中，已对超氧化物的产生进行了测定。尽管胞质酶确实会产生超氧阴离子，但较大部分是由呼吸电子传递链的组分自动氧化产生的。在37摄氏度且氧分压、NADH和NAD⁺水平与体内水平相匹配的情况下，进行呼吸作用的膜囊泡每传递10000个电子会产生3个超氧阴离子。这相当于在以葡萄糖为食的细胞中，细胞内超氧阴离子的产生速率为5微摩尔/秒。正常细胞中高含量的SOD将超氧阴离子的积累限制在2×10⁻¹⁰摩尔，从细胞膜到细胞中心存在适度的梯度。SOD缺陷型突变体的超氧阴离子稳态含量要高得多。某些酶被超氧化物介导失活的速率足够快，以至于即使是10⁻¹⁰摩尔的超氧阴离子也会施加显著的氧化应激。
