Regulation of Inducible Nitric Oxide Synthase by Self-Generated NO

Abu-Soûd, Husam M.; Ichimori, Kohji; Nakazawa, Hiroe; Stuehr, Dennis J.

doi:10.1021/bi010066m

Cited by 71 publications

(98 citation statements)

References 33 publications

(75 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Heme⅐NO buildup was fit to a two-exponential function. The amplitude of the initial exponential phase corresponded to a minority of the total iNOS (25%), and its rate was similar to that previously observed by Abu-Soud et al (29). Our data are consistent with heme⅐NO complex buildup and inhibition of NADPH consumption occurring by two processes in iNOS (28 -30): (a) an immediate process that involves near-geminate binding of newly formed NO to the ferric heme and then subsequent reduction to the ferrous heme⅐NO complex and (b) a subsequent process that involves ferric heme binding NO that accumulates in solution.…”

Section: Kinetic Characterization Of No Interactions With Inos and Ensupporting

confidence: 89%

“…This approximation does not precisely mimic in vitro conditions where NO degradation is complex and depends on the concentrations of NO, O 2 , and other factors. However, it allowed us to vary how much NO accumulated in the simulated reactions and check if our kinetic model could accurately account for the results of Abu-Soud et al (29), who varied NO buildup in solution using a superoxide generating system in his iNOS reactions. Fig.…”

Section: Kinetic Characterization Of No Interactions With Inos and Enmentioning

confidence: 99%

“…For example, iNOS displays a more gradual time course and smaller extent of NO inhibition compared with nNOS, its heme⅐NO complex is predominantly ferric instead of ferrous, and NO scavengers increase its activity (26 -29). Indeed, much inhibition associated with its heme⅐NO complex formation, as well as complex buildup itself, is directly related to the concentration of NO that is achieved in the reaction (29). On the other hand, Masters and colleagues (30) showed that a minor amount of ferrous heme⅐NO complex forms in iNOS during the first seconds after initiating NO synthesis, suggesting that its regulation also * The costs of publication of this article were defrayed in part by the payment of page charges.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Differences in Three Kinetic Parameters Underpin the Unique Catalytic Profiles of Nitric-oxide Synthases I, II, and III

Santolini

Meade

Stuehr

2001

Journal of Biological Chemistry

Self Cite

116

163

View full text Add to dashboard Cite

We previously reported the existence of a special autoregulation property of neuronal nitric-oxide synthase (NOS) based on NO near-geminate combination and partial trapping of neuronal NOS (nNOS) through a futile regenerating pathway. On this basis, we developed a kinetic simulation model that was proven to predict nNOS catalytic specificities and mutations effects (San- The free radical nitric oxide (NO) 1 is involved in an increasing number of physiologic and pathophysiologic processes (1-6). NO is generated by the NO synthases, which are found in numerous organisms. Animal NO synthases are homodimers whose subunits are comprised of a reductase domain containing FAD, FMN, and NADPH binding sites, and an oxygenase domain containing 6(R)-tetrahydrobiopterin (H 4 B), iron protoporphyrin IX (heme), and a binding site for the L-arginine (Arg) substrate (7,8). NO synthases catalyze two sequential mixedfunction oxidations, the first being Arg hydroxylation to form N -hydroxy-L-arginine (NOHA) as a bound intermediate (9 -11), and the second converting NOHA to citrulline and NO.toliniThree main NO synthases are expressed in mammals and differ in their functions, amino acid sequence, post-translational modification, and cellular location. Two NOS, neuronal NOS (nNOS or NOS-1) and endothelial NOS (eNOS or NOS-3), are constitutively expressed and involved in signal cascades. The third NOS is cytokine-inducible (iNOS or NOS-2) and functions as both a regulator and effector of the immune response. The counterpart to this diversity of location and function is a specific regulation of each isoform. For example, NO synthases differ significantly regarding Ca 2ϩ levels required to bind calmodulin (CaM), which triggers heme reduction and NO synthesis (12, 13). They also have different capacities to be upor down-regulated by serine/threonine phosphorylation (14, 15). A third difference involves regulation via heme⅐NO complex formation. In nNOS, we have established that heme⅐NO complex formation is an intrinsic feature that governs the rate of NO synthesis and shifts the enzyme apparent K m O 2 to a higher value (16,17). The model shown in Scheme 1 below can explain these effects (18). It incorporates the observation that ferric heme binds newly formed NO before it can leave the enzyme (19,20). This causes nNOS to partition between futile and productive cycles during catalysis (see Scheme 1), with only the productive cycle liberating NO (18). Key kinetic parameters for nNOS have been measured, including rates of heme reduction and NO dissociation, k cat , and oxidation of the ferrous heme⅐NO complex (19,21,22). These values are set such that a majority of nNOS exists as the ferrous heme⅐NO complex during steady-state NO synthesis (23,24). Computer simulation of the kinetic model in Scheme 1 reproduces this result and can accurately simulate the pre-steady-state and steady-state behaviors of nNOS mutants that display greater or diminished activity relative to wild-type enzyme (18,25).The available data for iNOS and eNOS suggest r...

show abstract

Section: Kinetic Characterization Of No Interactions With Inos and Ensupporting

confidence: 89%

Section: Kinetic Characterization Of No Interactions With Inos and Enmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Differences in Three Kinetic Parameters Underpin the Unique Catalytic Profiles of Nitric-oxide Synthases I, II, and III

Santolini

Meade

Stuehr

2001

Journal of Biological Chemistry

Self Cite

116

163

View full text Add to dashboard Cite

show abstract

“…The heme is ligated to a cysteine thiolate (5-7) and catalyzes a reductive activation of molecular oxygen in conjunction with H 4 B in each of the two steps of NO synthesis (8 -11). The NOS heme also binds self-generated NO as an intrinsic feature of catalysis (12)(13)(14). Each molecule of NO generated by NOS has a high probability of binding to the heme before it is released from the enzyme.…”

mentioning

confidence: 99%

A Conserved Val to Ile Switch near the Heme Pocket of Animal and Bacterial Nitric-oxide Synthases Helps Determine Their Distinct Catalytic Profiles

Wang

Wei

Sharma

et al. 2004

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

The rate of each transition was increased relative to wild-type bsNOS, with Fe III NO dissociation being 3.6 times faster. In V346I iNOSoxy we consecutively observed the beginning ferrous, Fe II O 2 , a mixture of Fe III NO and ferric heme species, and ending ferric enzyme. The rate of each transition was decreased relative to wild-type iNOSoxy, with the Fe III NO dissociation being 3 times slower. An independent measure of NO binding kinetics confirmed that V346I iNOSoxy has slower NO binding and dissociation than wild-type. Citrulline production by both mutants was only slightly lower than wild-type enzymes, indicating good coupling. Our data suggest that a greater shielding of the heme pocket caused by the Val/Ile switch slows down NO synthesis and NO release in NOS, and thus identifies a structural basis for regulating these kinetic variables.Nitric oxide synthases (NOSs) 1 are flavoheme enzymes that generate nitric oxide (NO) from L-arginine (Arg) (1, 2). The overall reaction consumes 1.5 NADPH and 2 O 2 and involves two steps, the first being Arg hydroxylation to form N-hydroxy-L-Arg (NOHA), and the second being NOHA oxidation to form citrulline and NO (see Scheme 1).The NOS heme is located in a catalytic "oxygenase" domain that also contains the binding sites for Arg and the essential redox cofactor (6R)-tetrahydrobiopterin (H 4 B) (3, 4). The heme is ligated to a cysteine thiolate (5-7) and catalyzes a reductive activation of molecular oxygen in conjunction with H 4 B in each of the two steps of NO synthesis (8 -11). The NOS heme also binds self-generated NO as an intrinsic feature of catalysis (12)(13)(14). Each molecule of NO generated by NOS has a high probability of binding to the heme before it is released from the enzyme. The resulting ferric heme-NO product complex (Fe III NO) has been observed to build up as a transient species during NOHA oxidation reactions catalyzed by NOS oxygenase domains (NOSoxy) when run in a stopped-flow spectrophotometer under single turnover conditions (9,13,14). These experiments also provided spectral and kinetic information regarding the formation of an initial ferrous heme-dioxy species (Fe II O 2 ), whose disappearance then coincides with k cat and formation of the transient Fe III NO product complex (see Scheme 2). Because dissociation of the Fe III NO product complex is required for NO to escape from the enzyme, it is an essential step for the biologic functions of animal NOSs. In fact, this dissociation rate is one of three key kinetic parameters that together determine the overall catalytic behavior of a given NOS (15,16). Slower rates of NO dissociation dispose the Fe III NO product complex toward its reduction during catalysis, which then places the ferrous heme-NO enzyme species into a futile cycle that does not release NO (Fig. 1). Interestingly, there is only a modest variation in Fe III NO dissociation rates among the three mammalian NOS isoforms, which range from 2 to 5 s Ϫ1 when measured in NOHA single turnover reactions at 10°C (16).Given the above, we...

show abstract

“…For example, medial VSM cells in the arterial vessel wall exist in a chronic state of hypoxia that is increased during vascular diseases [132]. This would be inconsistent with the production of large amounts of iNOSderived NO because the K m of iNOS for molecular oxygen approximates 130 µM [1]. The bioavailability of L-arginine is also an important regulator of iNOS activity in vivo.…”

Section: Regulation Of Inos Activity and Expressionmentioning

confidence: 99%

Regulation of smooth muscle by inducible nitric oxide synthase and NADPH oxidase in vascular proliferative diseases

Ginnan

Guikema

Halligan

et al. 2008

Free Radical Biology and Medicine

View full text Add to dashboard Cite

Inflammation plays a critical role in promoting smooth muscle migration and proliferation during vascular diseases such as post-angioplasty restenosis and atherosclerosis. Another common feature of many vascular diseases is the contribution of reactive oxygen (ROS) and nitrogen (RNS) species to vascular injury. Primary sources of ROS and RNS in smooth muscle are several isoforms of NADPH oxidase (Nox) and the cytokine-regulated inducible nitric oxide (NO) synthase (iNOS). One important example of the interaction between NO and ROS is the reaction of NO with superoxide to yield peroxynitrite, which may contribute to the pathogenesis of hypertension. In this review, we discuss the literature that supports an alternate possibility: Nox-derived ROS modulate NO bioavailability by altering the expression of iNOS. We highlight data showing co-expression of iNOS and Nox in vascular smooth muscle and demonstrating the functional consequences of iNOS and Nox during vascular injury. We describe the relevant literature demonstrating that the mitogen activated protein kinases (MAP kinases) are important modulators of pro-inflammatory cytokinedependent expression of iNOS. A central hypothesis discussed is that ROS-dependent regulation of the serine/threonine kinase protein kinase Cδ (PKCδ) is essential to understanding how Nox may regulate signaling pathways leading to iNOS expression. Overall, the integration of non-phagocytic NADPHoxidase with cytokine signaling in general and in vascular smooth muscle in particular is poorly understood and merit further investigation.

show abstract

Regulation of Inducible Nitric Oxide Synthase by Self-Generated NO

Cited by 71 publications

References 33 publications

Differences in Three Kinetic Parameters Underpin the Unique Catalytic Profiles of Nitric-oxide Synthases I, II, and III

Differences in Three Kinetic Parameters Underpin the Unique Catalytic Profiles of Nitric-oxide Synthases I, II, and III

A Conserved Val to Ile Switch near the Heme Pocket of Animal and Bacterial Nitric-oxide Synthases Helps Determine Their Distinct Catalytic Profiles

Regulation of smooth muscle by inducible nitric oxide synthase and NADPH oxidase in vascular proliferative diseases

Contact Info

Product

Resources

About