Hecker M, Walsh D T, Vane J R
William Harvey Research Institute, St. Bartholomew's Hospital Medical College, London, England.
J Cardiovasc Pharmacol. 1992;20 Suppl 12:S139-41. doi: 10.1097/00005344-199204002-00039.
The nitric oxide (NO) synthase activity present in murine J774.2 monocyte/macrophages was characterized in terms of its intracellular localization, substrate specificity, and Ca2+ dependency. Traces of constitutive NO synthase activity were found in the microsomal fraction from noninduced J774.2 cells, whereas no NO synthase activity was detected in the cytosol. After 24 h in the presence of bacterial lipopolysaccharide and mouse interferon, NO synthase activity was substantially increased in both fractions with 51-60% of the total activity present in the cytosol. These activities, however, were clearly different, for the microsomal enzyme was Ca2+ dependent, whereas the cytosolic NO synthase was not. Moreover, NG-hydroxy-L-arginine (L-HOArg), L-homo-arginine, and several L-arginine (L-Arg)-containing dipeptides could replace L-Arg as substrates for the Ca(2+)-independent NO synthase, whereas the Ca(2+)-dependent enzyme accepted only L-Arg, L-HOArg, or L-Arg-L-Arg as substrates. Thus, a microsomal Ca(2+)-dependent NO synthase is induced in J774.2 monocyte/macrophages with a substrate specificity different from the inducible Ca(2+)-independent NO synthase as well as the constitutive NO synthase in, for example, endothelial cells. Irrespective of their intracellular localization, therefore, at least three isoforms of NO synthase exist, all of which can accommodate substrates different from L-Arg in size, charge, and hydrophobicity.
对小鼠J774.2单核细胞/巨噬细胞中存在的一氧化氮（NO）合酶活性，从其细胞内定位、底物特异性和Ca2+依赖性方面进行了表征。在未诱导的J774.2细胞的微粒体部分中发现了微量的组成型NO合酶活性，而在细胞质中未检测到NO合酶活性。在细菌脂多糖和小鼠干扰素存在下培养24小时后，两个部分中的NO合酶活性均显著增加，其中51 - 60%的总活性存在于细胞质中。然而，这些活性明显不同，因为微粒体酶依赖Ca2+，而细胞质中的NO合酶则不依赖Ca2+。此外，NG-羟基-L-精氨酸（L-HOArg）、L-高精氨酸和几种含L-精氨酸（L-Arg）的二肽可以替代L-Arg作为不依赖Ca(2+)的NO合酶的底物，而依赖Ca(2+)的酶只接受L-Arg、L-HOArg或L-Arg-L-Arg作为底物。因此，在J774.2单核细胞/巨噬细胞中诱导出了一种微粒体Ca(2+)-依赖性NO合酶，其底物特异性不同于诱导型不依赖Ca(2+)的NO合酶以及例如内皮细胞中的组成型NO合酶。因此，无论其细胞内定位如何，至少存在三种NO合酶同工型，所有这些同工型都能容纳在大小、电荷和疏水性方面不同于L-Arg的底物。
