Brüne B, Lapetina E G
Faculty of Biology, University of Konstanz, Germany.
Genet Eng (N Y). 1995;17:149-64.
Nitric oxide signaling is achieved through cGMP-dependent and -independent mechanisms. The latter are exemplified by the NAD(+)-dependent automodification of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The experimental post-translational, covalent modification of the enzyme by [32P]NAD+ is achieved using NO-releasing compounds and an active constitutive or inducible NO-synthase. Potential roles for NO in this covalent enzyme modification can be grouped as follows: S-Nitrosylation of GAPDH by NO+ NAD(+)-dependent, post-translational covalent automodification of GAPDH. Oxidative modification of GAPDH by NO-related compounds, probably ONOO. GAPDH modification by one of the proposed mechanisms would lead to inhibition of enzyme catalysis. It is likely that the NAD(+)-dependent automodification process occurs in vitro, in intact cells, and in whole animals. Besides its normal function in glycolysis, GAPDH not only is a target for NO-mediated direct and indirect modifications but also is ADP-ribosylated in the presence of brefeldin A (90). The relation of such ADP-ribosylation to enzyme activity is so far unknown. GAPDH also may be involved in one of the following functions unrelated to its glycolytic activity (81 and refs. therein; 90): binding and transport of tRNA associated with nuclear localization of GAPDH. DNA-repair activity, i.e., uracil DNA glycosylase. Activation of transcription in neurons. Interaction with tubulin and microtubules. The transport of nitric oxide. Serves as a substrate for brefeldin A stimulated ADP-ribosylation. Because some of these alternative functions of GAPDH, just like NO-mediated modification of the enzyme, are related to the NAD+ binding site of the protein, we are interested in searching for the significance of these activities in relation to NO actions. In recent years, several functions of NO have been linked to direct, cGMP-independent actions. Modification of GAPDH is probably just one interesting target related to NO-redox chemistry and active-site thiol modification. It will be challenging to investigate NO biochemistry in closer detail and to elucidate how NO targets biological systems, especially in relation to the patho-physiological role of NO in medically related conditions.
一氧化氮信号传导是通过依赖cGMP和不依赖cGMP的机制实现的。后者的例证是糖酵解酶甘油醛-3-磷酸脱氢酶（GAPDH）的NAD⁺依赖性自身修饰。使用释放NO的化合物以及活性组成型或诱导型一氧化氮合酶，可实现[³²P]NAD⁺对该酶进行实验性的翻译后共价修饰。NO在这种共价酶修饰中的潜在作用可归纳如下：NO对GAPDH的S-亚硝基化以及NAD⁺依赖性的GAPDH翻译后共价自身修饰。NO相关化合物（可能是过氧亚硝酸根）对GAPDH的氧化修饰。通过上述一种机制对GAPDH进行修饰会导致酶催化作用受到抑制。NAD⁺依赖性自身修饰过程很可能在体外、完整细胞以及整个动物体内发生。除了在糖酵解中的正常功能外，GAPDH不仅是NO介导的直接和间接修饰的靶点，而且在布雷菲德菌素A存在的情况下会发生ADP-核糖基化（90）。目前尚不清楚这种ADP-核糖基化与酶活性之间的关系。GAPDH还可能参与以下与其糖酵解活性无关的功能之一（81及其中的参考文献；90）：与GAPDH核定位相关的tRNA的结合和运输。DNA修复活性，即尿嘧啶DNA糖基化酶。神经元中的转录激活。与微管蛋白和微管的相互作用。一氧化氮的运输。作为布雷菲德菌素A刺激的ADP-核糖基化的底物。由于GAPDH的这些替代功能中的一些，就像NO介导的酶修饰一样，与蛋白质的NAD⁺结合位点有关，我们有兴趣研究这些活性与NO作用相关的意义。近年来，NO的几种功能已与直接的、不依赖cGMP的作用相关联。GAPDH的修饰可能只是与NO氧化还原化学和活性位点硫醇修饰相关的一个有趣靶点。更详细地研究NO生物化学并阐明NO如何作用于生物系统将具有挑战性，特别是在与医学相关病症中NO的病理生理作用方面。
