Nitric oxide synthase is a cytochrome P-450 type hemoprotein.
ABSTRACT Nitric oxide has emerged as an important mammalian metabolic intermediate involved in critical physiological functions such as vasodilation, neuronal transmission, and cytostasis. Nitric oxide synthase (NOS) catalyzes the five-electron oxidation of L-arginine to citrulline and nitric oxide. Cosubstrates for the reaction include molecular oxygen and NADPH. In addition, there is a requirement for tetrahydrobiopterin. NOS also contains the coenzymes FAD and FMN and demonstrates significant amino acid sequence homology to NADPH-cytochrome P-450 reductase. Herein we report the identification of the inducible macrophage NOS as a cytochrome P-450 type hemoprotein. The pyridine hemochrome assay showed that the NOS contained a bound protoporphyrin IX heme. The reduced carbon monoxide binding spectrum shows an absorption maximum at 447 nm indicative of a cytochrome P-450 hemoprotein. A mixture of carbon monoxide and oxygen (80%/20%) potently inhibited the reaction (73-79%), showing that the heme functions directly in the oxidative conversion of L-arginine to nitric oxide and citrulline. Additionally, partially purified NOS from rat cerebellum was inhibited by CO, suggesting that this isoform may also contain a P-450-type heme. NOS is the first example of a soluble cytochrome P-450 in eukaryotes. In addition, the presence of FAD and FMN indicates that this is the first catalytically self-sufficient mammalian P-450 enzyme, containing both a reductase and a heme domain on the same polypeptide.
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ABSTRACT: Background: Metabolic syndrome is a collection of ailments resulting in a higher risk of cardiovascular disease and type II diabetes mellitus. It also results in prolonged endothelial dysfunction which promotes hypertension. Objective: The current study examines the acute effect of carbon monoxide (CO) inhibition and nitric oxide (NO) stimulation in septal coronary arteries. Methods: These studies were conducted in inactin anesthetized obese and lean Zucker rats (13-14 weeks of age). Coronary arteries were isolated from obese and lean Zucker rats and in vitro experiments were conducted. Isolated coronary arteries were pre-treated with chromium mesoporphyrin (CrMP) which is a heme oxygenase inhibitor and L-arginine, a NO precursor. Results: Blood pressure, non-fasting blood glucose, HBCO, CO levels and Arginase I expression were higher in obese Zucker rats (ZR) as compared to the lean (L) group. Obese ZR had higher body, kidney and heart weights as compared to the LZR. Acetylcholine induced vasodilation was greatly attenuated in Obese ZR compared to the lean group. No differences in the diameters of the septal coronary artery were observed in both groups when treated with CrMP. However, pretreatment with L-arginine, abolished the differences between the groups. Conclusion: This study demonstrates the potential of NO induction to improve coronary blood flow during metabolic syndrome induced endothelial dysfunction, where alterations in CO levels appeared to have no significant coronary effects.03/2014; 2(1):8. DOI:10.14419/ijm.v2i1.1941
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ABSTRACT: ischemic preconditioning (IPC) protects against liver ischemia-reperfusion (IR) injury. The mechanism involves nitric oxide metabolism but the importance of endothelial nitric oxide synthase (eNOS) has not been established. Heme oxygenase-1 (HO-1) protects against liver IR but it is unclear if this depends on nitric oxide synthase. A mouse model of IPC with liver IR using wild-type (WT) and eNOS transgenic knockout (eNOS-/-) mice was developed to study the role of eNOS and its relationship to HO-1. Serum alanine aminotransferase level, liver histopathologic injury scores, and liver microcirculatory blood flow were measured. Western blots measured liver HO-1/2, eNOS, phosphorylated eNOS, inducible nitric oxide synthase, and reverse transcription-polymerase chain reaction (HO-1). A set of 24-h recovery experiments was undertaken on WT mice with measurement of serum alanine aminotransferase level, histologic injury score, and HO-1 by Western blot. In WT animals, IPC preceding IR resulted in a reduction in hepatocellular and histologic injury, and improvement in parenchymal perfusion. In contrast, IPC in the eNOS-/- model did not protect the animals from IR injury. There was no difference between the eNOS and phosphorylated eNOS expression in all the WT groups. HO-1 protein was not detected in the nonrecovery groups but HO-1 messenger RNA was detected in all groups. In WT recovery experiments, IPC was protective against IR injury. HO-1 protein was detected in the IPC + IR and IR only groups but not in the sham group. This study developed and used an eNOS-/- model to demonstrate that eNOS mediates protection against liver IR injury by IPC. The eNOS expression and activity and HO-1 expression are increased independently in liver IPC and IR, with HO-1 expression increased in the later stages of IPC and IR.Journal of Surgical Research 09/2013; 186(1). DOI:10.1016/j.jss.2013.08.019 · 2.12 Impact Factor
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ABSTRACT: The enzyme heme oxygenase (HO) degrades heme to form equimolar amounts of iron, biliverdin and carbon monoxide (CO). CO is a key regulatory factor of vascular tone. Thus, the current study was performed to evaluate the hypothesis that acute infusion of angiotensin II (AngII) promotes hypertension via an induction in heme oxygenase-1 (HO-1), which increases carbon monoxide (CO). Male Sprague Dawley rats (200 – 300g) were acutely treated with AngII (5ng/kg/min, IV), delta-aminolevulinic acid (DALA) (80 μmol/kg, IV) and zinc deuteroporphyrin 2, 4-bis glycol (ZnDPBG) (20mg/kg, IV) or vehicle. Hemodynamic and renal functions were evaluated. Blood pressure was significantly elevated in rats treated with AngII and AngII + DALA. HO-1 concentrations in hearts and kidneys were also elevated. Acute angiotensin II administration produced a significant increase in endogenous CO when compared to control. Urine flow (UF), glomerular filtration rate (GFR), sodium excretion (UNaV), and potassium excretion (UKV) were significantly decreased in AngII infused rats when compared to control. However, there were no significant changes in renal blood flow (RBF) among the groups. Animals treated with the HO-1 inhibitor, ZnDPBG (20mg/kg, IV), had reduced blood pressure and increased UF, GFR, UNaV, UKV when compared to AngII and AngII + DALA treated rats. Also, HO-1 protein levels in heart and kidney and carboxyhemoglobin levels were reduced in ZnDPBG treated animals. These results demonstrate that AngII infusion promotes hypertension via induction in HO-1, which increases carbon monoxide levels and inhibition of HO-1 with ZnDPBG decreases the blood pressure.