Endothelial nitric oxide synthase (eNOS), the enzyme that catalyzes the production of NO from the amino acid arginine in endothelial cells, plays a key role in vasoregulation

catalyzes the production of NO from the amino acid arginine in endothelial cells, plays a key role in vasoregulation as well as in other important physiological processes such as angiogenesis. Impaired production of endothelial NO has been associated with hypertension, heart failure, hypercholesterolemia, atherosclerosis and diabetes (Govers and Rabelink, 2001; Vallance and Chan, 2001; Maxwell, 2002). Circulating effectors, such as bradykinin, bind to receptors on the luminal surface of endothelial cells, signaling the transient release of NO to the adjacent smooth muscle layer and resulting in relaxation of the vessel wall. The signal for eNOS activation is a transient increase in intracellular calcium, which activates the enzyme through binding of a calcium–calmodulin complex (Ca–Cam). Endothelial NOS activation also occurs in response to shear stress (Govers and Rabelink, 2001; Maxwell, 2002). Consistent with the important physiological roles of eNOS, the enzyme appears to be subject to multiple modes of regulation, in addition to primary regulation through reversible Ca–Cam binding and activation. These include reversible phosphorylation and palmitoylation, substrate and cofactor availability, dimerization of enzyme subunits, intracellular translocation and protein–protein interactions (Govers and Rabelink, 2001). Several of these potential modes of regulation appear to be interrelated. As a component of caveolae, a subcompartment of the plasma membrane that serves to sequester proteins involved in cell signaling, eNOS may transiently interact with several different caveolar components. Previous work from several different laboratories has suggested that a diverse group of proteins, including calmodulin, caveolin-1, bradykinin B2 receptor, heat shock protein 90, argininosuccinate synthase (AS), argininosuccinate lyase (AL), Raf-1, Akt, extracellular signal-related kinase, 2083 The Journal of Experimental Biology 206, 2083-2087 © 2003 The Company of Biologists Ltd doi:10.1242/jeb.00361