Nitric-oxide dioxygenase activity and function of flavohemoglobins - Sensitivity to nitric oxide and carbon monoxide inhibition
Nitric-oxide dioxygenase activity and function of flavohemoglobins - Sensitivity to nitric oxide and carbon monoxide inhibition
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DOI：
10.1074/jbc.m004141200
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发表时间：
2000-10-13
影响因子：
4.8
通讯作者：
Riggs, AF
中科院分区：
文献类型：
--
作者：
Gardner, PR;Gardner, AM;Riggs, AF
广泛分布的黄素血红蛋白（flavohemoglobins，flavoHbs）作为NO双加氧酶起作用，并赋予细胞对NO毒性的抗性。来自酿酒酵母、真养产碱菌和大肠杆菌的FlavoHbs具有相似的光谱、O-2、NO和CO结合动力学以及稳态NO双加氧动力学。S的周转数（V-max）。cerevisiae，A. eutrophus和E.在37 ℃，200 μ M O-2条件下，大肠杆菌flavoHb分别为112，290和365 NO血红素（-1）s（-1）。NO的K-M值较低，范围为0.1 - 0.25 μ M。900-2900 μ M-1 s（-1）的V-max/K-M（NO）比表明了极其有效的二氧化机制。O-2的近似K-M值范围为60至90 μ M。当NO：O-2的比例大于或等于1：100时，NO抑制双加氧酶，并使真实的K-M（O-2）值难以确定。O-2和NO与还原的黄素Hbs（17-50 μ M-1 s（-1））结合的高且大致相等的二级速率常数和小的NO解离速率常数表明NO通过形成无活性的黄素HbNO复合物来抑制双加氧酶反应。一氧化碳还以高亲和力结合还原的flavoHbs，并相对于O-2竞争性抑制NO双加氧酶（K-I（CO）=类似于1 μ M）。这些结果表明，flavoHbs和相关的血红蛋白进化为氮代谢的NO解毒成分，能够区分O-2抑制NO和CO。
Widely distributed flavohemoglobins (flavoHbs) function as NO dioxygenases and confer upon cells a resistance to NO toxicity. FlavoHbs from Saccharomyces cerevisiae, Alcaligenes eutrophus, and Escherichia coli share similar spectra, O-2, NO, and CO binding kinetics, and steady-state NO dioxygenation kinetics. Turnover numbers (V-max) for S. cerevisiae, A. eutrophus, and E. coli flavoHbs are 112, 290, and 365 NO heme(-1) s(-1), respectively, at 37 degrees C with 200 mu M O-2. The K-M values for NO are low and range from 0.1 to 0.25 mu M. V-max/K-M(NO) ratios of 900-2900 mu M-1 s(-1) indicate an extremely efficient dioxygenation mechanism. Approximate K-M values for O-2 range from 60 to 90 mu M. NO inhibits the dioxygenases at NO:O-2 ratios of greater than or equal to 1:100 and makes true K-M(O-2) values difficult to determine, High and roughly equal second order rate constants for O-2 and NO association with the reduced flavoHbs (17-50 mu M-1 s(-1)) and small NO dissociation rate constants suggest that NO inhibits the dioxygenase reaction by forming inactive flavoHbNO complexes. Carbon monoxide also binds reduced flavoHbs with high affinity and competitively inhibits NO dioxygenases with respect to O-2 (K-I(CO) = similar to 1 mu M). These results suggest that flavoHbs and related hemoglobins evolved as NO detoxifying components of nitrogen metabolism capable of discriminating O-2 from inhibitory NO and CO.