The study by David S. Bredt and Solomon H. Snyder from the Johns Hopkins University School of Medicine focuses on the isolation and characterization of nitric oxide synthetase (NOS), an enzyme that converts arginine to nitric oxide (NO). NO plays crucial roles in vascular relaxation, cytotoxic actions of immune cells, and the influence of excitatory amino acids on cerebellar cyclic GMP. The researchers purified NOS 6000-fold to homogeneity from rat cerebellum using a 2',5'-ADP affinity column eluted with NADPH. They found that NOS activity requires calmodulin, a calcium-binding protein, and that the enzyme migrates as a single 150-kDa band on SDS/PAGE, suggesting it is a monomer. The purified NOS has high affinity for arginine and similar kinetic properties to other NADPH-requiring oxidative enzymes. The study also highlights the importance of calmodulin in explaining the calcium-dependent regulation of NOS activity, which has implications for understanding endothelium-mediated smooth muscle relaxation. The availability of homogeneous NOS preparations should facilitate further research on its molecular mechanism and immunohistochemical localization.The study by David S. Bredt and Solomon H. Snyder from the Johns Hopkins University School of Medicine focuses on the isolation and characterization of nitric oxide synthetase (NOS), an enzyme that converts arginine to nitric oxide (NO). NO plays crucial roles in vascular relaxation, cytotoxic actions of immune cells, and the influence of excitatory amino acids on cerebellar cyclic GMP. The researchers purified NOS 6000-fold to homogeneity from rat cerebellum using a 2',5'-ADP affinity column eluted with NADPH. They found that NOS activity requires calmodulin, a calcium-binding protein, and that the enzyme migrates as a single 150-kDa band on SDS/PAGE, suggesting it is a monomer. The purified NOS has high affinity for arginine and similar kinetic properties to other NADPH-requiring oxidative enzymes. The study also highlights the importance of calmodulin in explaining the calcium-dependent regulation of NOS activity, which has implications for understanding endothelium-mediated smooth muscle relaxation. The availability of homogeneous NOS preparations should facilitate further research on its molecular mechanism and immunohistochemical localization.