The three genetically encoded isoforms of nitric oxide synthase (NOS) in mammals are differentially expressed in various cells and tissues. Neuronal (nNOS) and endothelial (eNOS) isoforms are constitutively expressed and the inducible (iNOS) isoform is induced by various cytokines. Structural differences among these isoforms are being studied by a variety of biophysical techniques [electron paramagnetic spectroscopy (EPR), absorbance, fluorescence, and circular dichroism (CD) spectroscopy, and X-ray crystallography]. We have used optical difference spectroscopy to determine binding constants for substrate analogs and inhibitors of all three isoforms, and EPR to define the environment of the heme iron in each case. Spectral perturbations of each NOS isoform indicate that the heme environments are unique. Our studies have demonstrated that the binding of substrates and analogs affects the binding of ligands such as NO and CO to these isoforms. Utilization of these approaches permits further definition of the substrate- and hemebinding environments. Various modular constructs and mutants of the three isoforms have led to identification of modules of the isoforms involved in cofactor binding. Supported by NIH (GM52419 & HL30050) and by Welch Grant AQ 1192 to BSSM.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology