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.
"NOSs are hemoproteins with a cytochrome P450-like active site that catalyzes the oxidation of arginine to NO and citrulline (White and Marletta, 1992). To evaluate the contribution of NO to MC-LR-induced mutagenesis, A L cells were exposed to MC-LR for 30 days with or without L-NMMA, which competitively blocks the activity of NOSs in cells (Hong et al., 2010). "
"Alternatively, previous literature demonstrated that CO promotes endothelium dependent vasoconstriction by inhibiting endothelial NO formation (Johnson & Johnson 2003) thus attenuating the vasodilatory effects of the nitric oxide system (White & Marletta 1992, Thorup et al. 1999). Taken together, this suggests that CO and NO play crucial roles as regulators of normal vascular tone. "
[Show abstract][Hide abstract] 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.
"NO donors can activate the HO-1 gene expression and activity in a variety of tissues  . Conversely HO-1 activity can modulate NOS activity . The relationship between HO-1 and eNOS in liver IPC and IR injury is currently unclear. "
[Show abstract][Hide abstract] 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 · 1.94 Impact Factor
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