Sreider C M, Grinblat L, Stoppani A O
Centro de Investigaciones Bioenergéticas, Facultad de Medicina, Buenos Aires, Argentina.
Biochem Pharmacol. 1990 Oct 15;40(8):1849-57. doi: 10.1016/0006-2952(90)90366-s.
Heart lipoamide dehydrogenase (LADH) catalyzed redox-cycling and O2-. production by (5-nitro-2-furfurylidene)amino derivatives using NADH as electron donor. NADH was a much more effective electron donor than NADPH for the nitroreductase activity. O2-. production was demonstrated by cytochrome c reduction, adrenochrome formation and the effect of superoxide dismutase. Under optimum conditions, nitroreductase activity was about 1% of LADH activity. One electron oxygen reduction and NADH oxidation correlated in 2:1 stoichiometry. The nitroreductase kinetics was in accordance with an ordered bi-bi mechanism. Nitrofuran derivatives bearing unsaturated five- or six-membered nitrogen heterocycles were more effective substrates than those bearing other groups, namely nifurtimox, nitrofurazone, nitrofurantoin and 5-nitro-2-furoic acid. Other nitro compounds (chloramphenicol, benznidazole, 2-nitroimidazole and 5-nitroindole) were ineffective. With the triazole, traizine and imidazole nitrofuran derivatives, the nitroreductase pH curve showed a maximum at pH 8.8, different from the pH optimum for the lipoamide reductase and diaphorase activities. Spectroscopic observations demonstrated pH-dependent structural changes in the triazole(I) and triazine derivatives which would affect their behavior as nitroreductase substrates. The nitroreductase activity was inhibited by p-chloromercuribenzoate and enhanced by cadmium and arsenite, whereas the NADH-induced LADH inactivation failed to affect the nitroreductase activity. In the absence of oxygen. LADH catalyzed nitrofuran reduction to products more reduced than the nitroanion, which were not reoxidized by oxygen. The anaerobic nitrofuran reduction was inhibited by cadmium and arsenite. The assayed nitrofuran compounds did not inhibit LADH lipoamide reductase activity, at variance with their action on glutathione reductase (Grinblat et al., Biochem Pharmacol 38: 767-772, 1989).
心脏硫辛酰胺脱氢酶（LADH）以NADH作为电子供体，催化（5-硝基-2-糠叉基）氨基衍生物的氧化还原循环和超氧阴离子（O₂⁻）生成。对于硝基还原酶活性而言，NADH是比NADPH更有效的电子供体。通过细胞色素c还原、肾上腺色素形成以及超氧化物歧化酶的作用证明了超氧阴离子（O₂⁻）的生成。在最佳条件下，硝基还原酶活性约为LADH活性的1%。单电子氧还原和NADH氧化以2:1的化学计量比相关。硝基还原酶动力学符合有序双底物双产物机制。带有不饱和五元或六元氮杂环的硝基呋喃衍生物比带有其他基团的更有效底物，即硝呋替莫、呋喃西林、呋喃妥因和5-硝基-2-糠酸。其他硝基化合物（氯霉素、苯硝唑、2-硝基咪唑和5-硝基吲哚）无效。对于三唑、三嗪和咪唑硝基呋喃衍生物，硝基还原酶的pH曲线在pH 8.8处出现最大值，这与硫辛酰胺还原酶和双氢硫辛酰胺脱氢酶活性的最适pH不同。光谱观察表明三唑（I）和三嗪衍生物中存在pH依赖性结构变化，这会影响它们作为硝基还原酶底物的行为。对氯汞苯甲酸抑制硝基还原酶活性，镉和亚砷酸盐增强该活性，而NADH诱导的LADH失活并未影响硝基还原酶活性。在无氧条件下，LADH催化硝基呋喃还原为比硝基阴离子还原程度更高的产物，这些产物不会被氧气再氧化。厌氧条件下的硝基呋喃还原受到镉和亚砷酸盐的抑制。所检测的硝基呋喃化合物不抑制LADH硫辛酰胺还原酶活性，这与它们对谷胱甘肽还原酶的作用不同（格林布拉特等人，《生物化学与药物学》38: 767 - 772, 1989）。
