Neuronal nitric oxide synthase isoforms α and μ are closely related calpain-sensitive proteins
Neuronal nitric oxide synthase isoforms α and μ are closely related calpain-sensitive proteins
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DOI：
10.1124/mol.54.2.305
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发表时间：
1998-08-01
影响因子：
3.6
通讯作者：
de Montellano, PRO
中科院分区：
文献类型：
--
作者：
Lainé, R;de Montellano, PRO
在横纹肌中表达的神经元一氧化氮合酶亚型 nNOS mu 与主要脑亚型 nNOS α 的不同之处在于在钙调蛋白和黄素结合结构域之间插入了 34 个氨基酸残基 [J Biol Chem 271:11204-11208 (1996)]。我们在此表明，尽管插入了肽，重组、纯化的 nNOS mu 仍具有与 nNOS α 相同的光谱特性、L-精氨酸 k(cat) 和 K-m 值、最佳 pH 值以及钙调蛋白结合亲和常数。然而，nNOS mu 消耗 NADPH 并减少细胞色素 c 的速度大约是 nNOS α 的一半。大鼠脑和肌肉匀浆对两种蛋白质的降解速率表明，nNOS mu 的降解速度比 nNOS α 慢。 nNOS(α) 和 nNOS mu 的体外半衰期分别为 12 和 50 分钟，钙蛋白酶对于这种降解很重要。这些短的体外半衰期表明 nNOS 亚型容易在体内快速降解。杜氏肌营养不良症患病肌肉组织中钙蛋白酶水平升高（20 倍），以及 nNOS mu 和 nNOS α 对这种酶的水解敏感性，可能导致患病组织中 nNOS 活性的缺乏。
The neuronal nitric oxide synthase isoform nNOS mu, which is expressed in striated muscle, differs from nNOS alpha, the major brain isoform, by the insertion of 34 amino acid residues between the calmodulin- and flavin-binding domains [J Biol Chem 271:11204-11208 (1996)]. We show here that recombinant, purified nNOS mu, despite the peptide insertion, has the same spectroscopic properties, L-arginine k(cat) and K-m values, optimal pH, and calmodulin binding affinity constant as nNOS alpha. However, nNOS mu consumes NADPH and reduces cytochrome c at approximately half the rate of nNOS alpha. The rates of degradation of the two proteins by rat brain and muscle homogenates show that nNOS mu is degraded more slowly than nNOS alpha. The in vitro half-lives of nNOS(alpha) and nNOS mu are 12 and 50 min, respectively, and calpain is important for this degradation. These short in vitro half-lives suggest that the nNOS isoforms are susceptible to rapid degradation in vivo. The elevated (20-fold) levels of calpain in diseased muscle tissue in Duchenne muscular dystrophy, and the hydrolytic sensitivity of both nNOS mu, and nNOS alpha to this enzyme, may contribute to the deficiency of nNOS activity in the diseased tissue.