Wade M L, Fitzpatrick F A
Huntsman Cancer Institute, University of Utah, Salt Lake City, Utah 84112, USA.
Arch Biochem Biophys. 1997 Nov 15;347(2):174-80. doi: 10.1006/abbi.1997.0348.
Nitric oxide modulates the activity of the hemoprotein isomerase enzymes that transform prostaglandin H2 into prostaglandin I2 and thromboxane A2. Two nitric oxide donors, 1-hexanamine, 6-(2hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-nitroso- hydrazine (MMNN) and 1,1-diethyl-2-hydroxy-2-nitrosohydrazine, modulated prostaglandin I2 synthase activity in a bidirectional manner. At moderate concentrations, they increased enzyme activity irreversibly and at higher concentrations they inhibited enzyme activity reversibly. We confirmed that these effects originated from nitric oxide. First, we showed that hemoglobin, a substance that sequesters nitric oxide, prevented both the activation and the inhibition of catalysis, stoichiometrically. Second, we showed that solutions depleted of nitric oxide had no effect on catalysis. Nitric oxide also modulated thromboxane A2 synthase activity; however, its effects on thromboxane A2 synthase differed from its effects on prostaglandin I2 synthase in three ways: (i) It inhibited thromboxane A2 synthase in a concentration-dependent manner. The IC50 = 4.2 +/- 0.8 microM MMNN corresponded to an IC50 congruent with 0.1-0.3 microM nitric oxide. (ii) It did not increase thromboxane A2 synthase activity at any concentration tested. (iii) Its irreversible inhibition of thromboxane A2 synthase contrasted with its reversible inhibition of prostaglandin I2 synthase. Nitric oxide also inhibited cellular formation of thromboxane A2 by intact platelets in a concentration-dependent manner. The IC50 = 267 +/- 26 microM MMNN corresponded to an IC50 congruent with 6-18 microM nitric oxide. We conclude that nitric oxide can modulate certain hemoprotein enzymes in the biosynthetic cascade that governs the formation of eicosanoid mediators of thrombosis and hemostasis.
一氧化氮可调节血红素蛋白异构酶的活性，这些酶可将前列腺素H2转化为前列腺素I2和血栓素A2。两种一氧化氮供体，1-己胺、6-(2-羟基-1-甲基-2-亚硝基肼基)-N-甲基-亚硝基肼（MMNN）和1,1-二乙基-2-羟基-2-亚硝基肼，以双向方式调节前列腺素I2合酶的活性。在中等浓度下，它们不可逆地增加酶活性，而在较高浓度下则可逆地抑制酶活性。我们证实这些作用源自一氧化氮。首先，我们表明血红蛋白（一种能螯合一氧化氮的物质）能按化学计量比阻止催化作用的激活和抑制。其次，我们表明不含一氧化氮的溶液对催化作用无影响。一氧化氮还调节血栓素A2合酶的活性；然而，它对血栓素A2合酶的作用在三个方面不同于对前列腺素I2合酶的作用：（i）它以浓度依赖性方式抑制血栓素A2合酶。MMNN的IC50 = 4.2±0.8 microM，相当于一氧化氮的IC50约为0.1 - 0.3 microM。（ii）在任何测试浓度下它都不会增加血栓素A2合酶的活性。（iii）它对血栓素A2合酶的不可逆抑制与对前列腺素I2合酶的可逆抑制形成对比。一氧化氮还以浓度依赖性方式抑制完整血小板中血栓素A2的细胞形成。MMNN的IC50 = 267±26 microM，相当于一氧化氮的IC50约为6 - 18 microM。我们得出结论，一氧化氮可调节生物合成级联反应中的某些血红素蛋白酶，该级联反应控制着血栓形成和止血的类花生酸介质的形成。
