Nitric oxide and myoglobins

Re-evaluation of potassium nitrite (E 249) and sodium nitrite (E 250) as food additives

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re-evaluating the safety of potassium nitrite (E 249) and sodium nitrite (E 250) when used as food additives. The ADIs established by the SCF (1997) and by JECFA (2002) for nitrite were 0-0.06 and 0-0.07 mg/kg bw per day, respectively. The available information did not indicate in vivo genotoxic potential for sodium and potassium nitrite. Overall, an ADI for nitrite per se could be derived from the available repeated dose toxicity studies in animals, also considering the negative carcinogenicity results. The Panel concluded that an increased methaemoglobin level, observed in human and animals, was a relevant effect for the derivation of the ADI. The Panel, using a BMD approach, derived an ADI of 0.07 mg nitrite ion/kg bw per day. The exposure to nitrite resulting from its use as food additive did not exceed this ADI for the general population, except for a slight exceedance in children at the highest percentile. The Panel assessed the endogenous formation of nitrosamines from nitrites based on the theoretical calculation of the NDMA produced upon ingestion of nitrites at the ADI and estimated a MoE > 10,000. The Panel estimated the MoE to exogenous nitrosamines in meat products to be < 10,000 in all age groups at high level exposure. Based on the results of a systematic review, it was not possible to clearly discern nitrosamines produced from the nitrite added at the authorised levels, from those found in the food matrix without addition of external nitrite. In epidemiological studies there was some evidence to link (i) dietary nitrite and gastric cancers and (ii) the combination of nitrite plus nitrate from processed meat and colorectal cancers. There was evidence to link preformed NDMA and colorectal cancers.

Determination of critical levels of residual oxygen to minimize discoloration of sliced packaged Norwegian salami under light display

Discoloration of sliced packaged salami is contributing to rejection of the product, food waste and economical loss. A combination of residual O₂ in the headspace of packages and light is causing photooxidation and deterioration of colour. The aim of this study was to establish maximum tolerable concentrations of residual O₂ in packages of salami slices with 100% N₂ under light display at 4 and 20°C. Salami sausages had variable inherent O₂ consumption rate. Storage of salami in 1% O₂ in darkness did not induce discoloration. The upper limits for O₂ for avoiding discoloration under light were variable in the range 0.1-1.0%, depending on temperature and type of salami. Display at 20°C increased the rate of O₂ depletion compared to 4°C. To minimize discoloration, sliced and packaged salami should be stored in darkness at approximately 20°C until the level of residual O₂ is reduced below a critical limit.

A cobalt–nitrosyl complex with a hindered hydrotris(pyrazolyl)borate coligand: detailed electronic structure, and reactivity towards dioxygen

The cobalt–nitrosyl complex [Co(NO)(L3)] is supported by a highly hindered tridentate nitrogen ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3⁻), and shows a linear Co–N–O unit.

Mechanistic Insight into the Nitric Oxide Dioxygenation Reaction of Nonheme Iron(III)-Superoxo and Manganese(IV)-Peroxo Complexes

Reactions of nonheme Fe(III) -superoxo and Mn(IV) -peroxo complexes bearing a common tetraamido macrocyclic ligand (TAML), namely [(TAML)Fe(III) (O2 )](2-) and [(TAML)Mn(IV) (O2 )](2-) , with nitric oxide (NO) afford the Fe(III) -NO3 complex [(TAML)Fe(III) (NO3 )](2-) and the Mn(V) -oxo complex [(TAML)Mn(V) (O)](-) plus NO2 (-) , respectively. Mechanistic studies, including density functional theory (DFT) calculations, reveal that M(III) -peroxynitrite (M=Fe and Mn) species, generated in the reactions of [(TAML)Fe(III) (O2 )](2-) and [(TAML)Mn(IV) (O2 )](2-) with NO, are converted into M(IV) (O) and (.) NO2 species through O-O bond homolysis of the peroxynitrite ligand. Then, a rebound of Fe(IV) (O) with (.) NO2 affords [(TAML)Fe(III) (NO3 )](2-) , whereas electron transfer from Mn(IV) (O) to (.) NO2 yields [(TAML)Mn(V) (O)](-) plus NO2 (-) .

Image Analysis and High Dimensional Control Chart for Inspection of Sausage Color Homogeneity and Uniformity

Sausage color usually influences consumers’ selection due to the perceptions of quality. Extensive studies have applied image processing to capture the characteristics of food products according to the high-dimensional nature of the resultant images. However, the color homogeneity (i. e. “within pack” variation) and uniformity (i. e. “between-pack” variation) have rarely been studied. Therefore, this paper proposes a new framework to detect both variations using images. In addition, a new approach has been developed to deal with high-dimension data involving colorimetric characteristics, namely L*, a*, b*, hue (h) and chroma (C*). These high-dimensional data are transformed to represent color homogeneity and uniformity. Hotelling T2 chart is used to detect color abnormalities. Our approach indicates that the out-of-control items can be identified with the control chart signals. Nonetheless, the out-of-control signals alone are inadequate for determination of the possible causes. Then, the proposed analysis framework was subsequently applied to identify possible causes that contributed to the process deviations. Furthermore, prior to the experiments with sausages, the image inspection device was tested for gauge repeatability and reproducibility.

Factors That Control the Reactivity of Cobalt(III)-Nitrosyl Complexes in Nitric Oxide Transfer and Dioxygenation Reactions: A Combined Experimental and Theoretical Investigation

Metal-nitrosyl complexes are key intermediates involved in many biological and physiological processes of nitric oxide (NO) activation by metalloproteins. In this study, we report the reactivities of mononuclear cobalt(III)-nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(14-TMC)Co(III)(NO)](2+) and [(12-TMC)Co(III)(NO)](2+), in NO-transfer and dioxygenation reactions. The Co(III)-nitrosyl complex bearing 14-TMC ligand, [(14-TMC)Co(III)(NO)](2+), transfers the bound nitrosyl ligand to [(12-TMC)Co(II)](2+) via a dissociative pathway, {[(14-TMC)Co(III)(NO)](2+) → {(14-TMC)Co···NO}(2+)}, thus affording [(12-TMC)Co(III)(NO)](2+) and [(14-TMC)Co(II)](2+) as products. The dissociation of NO from the [(14-TMC)Co(III)(NO)](2+) complex prior to NO-transfer is supported experimentally and theoretically. In contrast, the reverse reaction, which is the NO-transfer from [(12-TMC)Co(III)(NO)](2+) to [(14-TMC)Co(II)](2+), does not occur. In addition to the NO-transfer reaction, dioxygenation of [(14-TMC)Co(III)(NO)](2+) by O2 produces [(14-TMC)Co(II)(NO3)](+), which possesses an O,O-chelated nitrato ligand and where, based on an experiment using (18)O-labeled O2, two of the three O-atoms in the [(14-TMC)Co(II)(NO3)](+) product derive from O2. The dioxygenation reaction is proposed to occur via a dissociative pathway, as proposed in the NO-transfer reaction, and via the formation of a Co(II)-peroxynitrite intermediate, based on the observation of phenol ring nitration. In contrast, [(12-TMC)Co(III)(NO)](2+) does not react with O2. Thus, the present results demonstrate unambiguously that the NO-transfer/dioxygenation reactivity of the cobalt(III)-nitrosyl complexes bearing TMC ligands is significantly influenced by the ring size of the TMC ligands and/or the spin state of the cobalt ion.

Nitrate reductase activity of Staphylococcus carnosus affecting the color formation in cured raw ham

The influence of the nitrate reductase activity of two Staphylococcus carnosus strains used as starter cultures on the formation of nitrate, nitrite and color pigments in cured raw ham was investigated. In this context, microbiological, chemical and multivariate image analyses were carried out on cured raw hams, which were injected with different brines containing either nitrite or nitrate, with or without the S. carnosus starter cultures. During processing and storage, the viable counts of staphylococci remained constant at 6.5logcfu/g in the hams inoculated with starter cultures, while the background microbiota of the hams processed without the starter cultures developed after 14days. Those cured hams inoculated with S. carnosus LTH 7036 (high nitrate reductase activity) showed the highest decrease in nitrate and high nitrite concentrations in the end product, but were still in the range of the legal European level. The hams cured with nitrate and without starter culture or with the other strain, S. carnosus LTH 3838 (low nitrate reductase activity) showed higher residual nitrate levels and a lower nitrite content in the end product. The multivariate image analysis identified spatial and temporal differences in the meat pigment profiles of the differently cured hams. The cured hams inoculated with S. carnosus LTH 3838 showed an uncured core due to a delay in pigment formation. Therefore, the selection of starter cultures based on their nitrate reductase activity is a key point in the formation of curing compounds and color pigments in cured raw ham manufacture.

Effect of Outer-Sphere Side Chain Substitutions on the Fate of the trans Iron-Nitrosyl Dimer in Heme/Nonheme Engineered Myoglobins (Fe(B)Mbs): Insights into the Mechanism of Denitrifying NO Reductases

Denitrifying NO reductases are transmembrane protein complexes that utilize a heme/nonheme diiron center at their active sites to reduce two NO molecules to the innocuous gas N2O. Fe(B)Mb proteins, with their nonheme iron sites engineered into the heme distal pocket of sperm whale myoglobin, are attractive models for studying the molecular details of the NO reduction reaction. Spectroscopic and structural studies of Fe(B)Mb constructs have confirmed that they reproduce the metal coordination spheres observed at the active site of the cytochrome c-dependent NO reductase from Pseudomonas aeruginosa. Exposure of Fe(B)Mb to excess NO, as examined by analytical and spectroscopic techniques, results primarily in the formation of a five-coordinate heme-nitrosyl complex without N2O production. However, substitution of the outer-sphere residue Ile107 with a glutamic acid (i.e., I107E) decreases the formation rate of the five-coordinate heme-nitrosyl complex and allows for the substoichiometric production of N2O. Here, we aim to better characterize the formation of the five-coordinate heme-nitrosyl complex and to explain why the level of N2O production increases with the I107E substitution. We follow the formation of the five-coordinate heme-nitrosyl inhibitory complex through the sequential exposure of Fe(B)Mb to different NO isotopomers using rapid-freeze-quench resonance Raman spectroscopy. The data show that the complex is formed by the displacement of the proximal histidine by a new NO molecule after the weakening of the Fe(II)-His bond in the intermediate six-coordinate low-spin (6cLS) heme-nitrosyl complex. These results lead us to explore diatomic migration within the scaffold of myoglobin and whether substitutions at residue 107 can be sufficient to control access to the proximal heme cavities. Results on a new Fe(B)Mb construct with an I107F substitution (Fe(B)Mb3) show an increased rate for the formation of the five-coordinate low-spin heme-nitrosyl complex without N2O production. Taken together, our results suggest that production of N2O from the [6cLS heme {FeNO}(7)/{Fe(B)NO}(7)] trans iron-nitrosyl dimer intermediate requires a proton transfer event facilitated by an outer-sphere residue such as E107 in Fe(B)Mb2 and E280 in P. aeruginosa cNOR.

Photo-antimicrobial polymeric films releasing nitric oxide with fluorescence reporting under visible light

A novel molecular hybrid has been embedded in poly(lactic-co-glycolic acid) to give an antibacterial film photogenerating NO with a concomitant fluorescent reporter.

Nitric oxide activation by distal redox modulation in tetranuclear iron nitrosyl complexes

A series of tetranuclear iron complexes displaying a site-differentiated metal center was synthesized. Three of the metal centers are coordinated to our previously reported ligand, based on a 1,3,5-triarylbenzene motif with nitrogen and oxygen donors. The fourth (apical) iron center is coordinatively unsaturated and appended to the trinuclear core through three bridging pyrazolates and an interstitial μ4-oxide moiety. Electrochemical studies of complex [LFe3(PhPz)3OFe][OTf]2 revealed three reversible redox events assigned to the Fe(II)4/Fe(II)3Fe(III) (-1.733 V), Fe(II)3Fe(III)/Fe(II)2Fe(III)2 (-0.727 V), and Fe(II)2Fe(III)2/Fe(II)Fe(III)3 (0.018 V) redox couples. Combined Mössbauer and crystallographic studies indicate that the change in oxidation state is exclusively localized at the triiron core, without changing the oxidation state of the apical metal center. This phenomenon is assigned to differences in the coordination environment of the two metal sites and provides a strategy for storing electron and hole equivalents without affecting the oxidation state of the coordinatively unsaturated metal. The presence of a ligand-binding site allowed the effect of redox modulation on nitric oxide activation by an Fe(II) metal center to be studied. Treatment of the clusters with nitric oxide resulted in binding of NO to the apical iron center, generating a {FeNO}(7) moiety. As with the NO-free precursors, the three reversible redox events are localized at the iron centers distal from the NO ligand. Altering the redox state of the triiron core resulted in significant change in the NO stretching frequency, by as much as 100 cm(-1). The increased activation of NO is attributed to structural changes within the clusters, in particular, those related to the interaction of the metal centers with the interstitial atom. The differences in NO activation were further shown to lead to differential reactivity, with NO disproportionation and N2O formation performed by the more electron-rich cluster.

Polystyrene Nanofiber Materials for Visible-Light-Driven Dual Antibacterial Action via Simultaneous Photogeneration of NO and O2((1)Δg)

This contribution reports on the preparation, characterization, and biological evaluation of electrospun polystyrene nanofiber materials engineered with a covalently grafted NO photodonor and ionically entangled tetracationic porphyrin and phthalocyanine photosensitizers. These photofunctional materials exhibit an effective and simultaneous photogeneration of two antibacterial species such as nitric oxide (NO) and singlet oxygen, O2((1)Δg) under illumination with visible light, as demonstrated by their direct detection using amperometric and time-resolved spectroscopic techniques. Dual-mode photoantibacterial action is demonstrated by antibacterial tests carried out on Escherichia coli.

Reactions of Co(III)-nitrosyl complexes with superoxide and their mechanistic insights

New Co(III)-nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(12-TMC)Co(III)(NO)](2+) (1) and [(13-TMC)Co(III)(NO)](2+) (2), were synthesized via [(TMC)Co(II)(CH3CN)](2+) + NO(g) reactions. Spectroscopic and structural characterization showed that these compounds bind the nitrosyl moiety in a bent end-on fashion. Complexes 1 and 2 reacted with KO2/2.2.2-cryptand to produce [(12-TMC)Co(II)(NO2)](+) (3) and [(13-TMC)Co(II)(NO2)](+) (4), respectively; these possess O,O'-chelated nitrito ligands. Mechanistic studies using (18)O-labeled superoxide ((18)O2(•-)) showed that one O atom in the nitrito ligand is derived from superoxide and the O2 produced comes from the other superoxide O atom. Evidence supporting the formation of a Co-peroxynitrite intermediate is also presented.

Investigation of reduction and tolerance capability of lactic acid bacteria isolated from kimchi against nitrate and nitrite in fermented sausage condition

Lactobacillus brevis KGR3111, Lactobacillus curvatus KGR 2103, Lactobacillus plantarum KGR 5105, and Lactobacillus sakei KGR 4108 isolated from kimchi were investigated for their potential to be used as starter culture for fermented sausages with the capability to reduce and tolerate nitrate/nitrite. The reduction capability of tested strains for nitrate was not dramatic. All tested strains, however, showed the capability to produce nitrite reductase with the reduction amount of 58.46-75.80 mg/l of NO(2)(-). L. brevis and L. plantarum showed nitrate tolerance with the highest number of 8.71 log cfu/ml and 8.81 log cfu/ml, and L. brevis and L. sakei exhibited nitrite tolerance with the highest number of 8.24 log cfu/ml and 8.25 log cfu/ml, respectively. As a result, L. brevis, L. plantarum, and L. sakei isolated from kimchi showed a tolerance against nitrate or nitrite with a good nitrite reduction capability, indicating the satisfaction of one of the selection criteria to be used as starter culture for fermented sausages.

Breast meat quality of broiler chickens can be affected by managing the level of nitric oxide

The objective of this study was to investigate the effects of nitric oxide (NO) on the quality of broiler chicken meat during postmortem storage. Eighteen broiler chickens were slaughtered and breast meat was randomly assigned to 1 of 3 treatments including the control group, nitric oxide synthase (NOS) inhibitor group, and NO enhancer group. The breast samples were incubated with water, NO enhancer, and NO inhibitor for 1 d and then stored at 4°C under atmospheric conditions for 4 and 7 d. Left side of breast meat was used to determine protein oxidation, lipid oxidation, water-holding capacity, and pH, whereas the right side was used for the measurement of color and drip loss. Breast meat from NO enhancer group showed the lowest water-holding capacity during refrigerated storage, whereas drip losses were not significantly (P > 0.05) different among 3 treatments. Lipid oxidation showed a significant difference (P < 0.05) only at 7 d in which NOS inhibitor group showed the highest, whereas the NO enhancer group showed the lowest levels of lipid oxidation. Carbonyl content in NO enhancer group was significantly higher than the control and NOS inhibitor treatment at 1 and 4 d of refrigerated storage. Lightness of breast meat in the NOS inhibitor group was greater, whereas redness was lower than the control and NO enhancer group at 4 and 7 d of refrigerated storage. The ultimate pH of 3 treatments was not significantly (P > 0.05) different from one another. These data indicate that NO could play a significant role in modulating the quality of fresh broiler breast meat during refrigerated storage.

Reactions of a chromium(III)-superoxo complex and nitric oxide that lead to the formation of chromium(IV)-oxo and chromium(III)-nitrito complexes

The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [Cr(III)(14-TMC)(O2)(Cl)](+), with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [Cr(IV)(14-TMC)(O)(Cl)](+), via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from electron paramagnetic resonance spectroscopy, computational chemistry and the observation of phenol nitration chemistry. The Cr(IV)-oxo complex does not react with nitrogen dioxide (NO2), but reacts with NO to afford a Cr(III)-nitrito complex, [Cr(III)(14-TMC)(NO2)(Cl)](+). The Cr(IV)-oxo and Cr(III)-nitrito complexes were also characterized spectroscopically and/or structurally.

Binding of O2 and NO to heme in heme-nitric oxide/oxygen-binding (H-NOX) proteins. A theoretical study

The binding of O2 and NO to heme in heme-nitric oxide/oxygen-binding (H-NOX) proteins has been investigated with DFT as well as dispersion-corrected DFT methods. The local protein environment was accounted for by including the six nearest surrounding residues in the studied systems. Attention was also paid to the effects of the protein environment, particularly the distal Tyr140, on the proximal iron-histidine (Fe-His) binding. The Heme-AB (AB = O2, NO) and Fe-His binding energies in iron porphyrin FeP(His)(AB), myoglobin Mb(AB), H-NOX(AB), and Tyr140 → Phe mutated H-NOX[Y140F(AB)] were determined for comparison. The calculated stabilization of bound O2 is even higher in H-NOX than that in a myoglobin (Mb), consistent with the observation that the H-NOX domain of T. tengcongensis has a very high affinity for its oxygen molecule. Among the two different X-ray crystal structures for the Tt H-NOX protein, the calculated results for both AB = O2 and NO appear to support the crystal structure with the PDB code 1XBN , where the Trp9 and Asn74 residues do not form a hydrogen-bonding network with Tyr140. A hydrogen bond interaction from the polar residue does not have obvious effects on the Fe-His binding strength, but a dispersion contribution to Ebind(Fe-His) may be significant, depending on the crystal structure used. We speculate that the Fe-His binding strength in the deoxy form of a native protein could be an important factor in determining whether the bond of His to Fe is broken or maintained upon binding of NO to Fe.

Photophysical and ligand binding studies of metalloporphyrins bearing hydrophilic distal superstructure

UV-vis absorption and emission studies on zinc and iron porphyrin complexes bearing H-bonding distal superstructures have been performed in two different organic solvents- tetrahydrofuran (THF) (coordinating) and dichloromethane (DCM) (non-coordinating). Quantum yields and lifetimes have been measured for these complexes which are in good agreement with the other reported metalloporphyrins. Binding affinities with anionic ligands such as N3- , CN- , S-2 , F- were monitored for these two complexes in aqueous media and the respective binding constant values were calculated. The Zn complex shows more selectivity towards cyanide while the Fe complex shows more selectivity towards azide.

Formation and identification of nitrosylmyoglobin by Staphylococcus xylosus in raw meat batters: a potential solution for nitrite substitution in meat products

Staphylococcus xylosus and Pediococcus pentosaceus isolated from Chinese dried sausage were assessed for their ability to convert metmyoglobin into nitrosylmyoglobin in Mann-Rogosa-Sharp broth model systems and raw pork meat batters without the addition of nitrite. The results showed that samples in model systems with S. xylosus cultures had an absorption spectra that is typical of nitrosylmyoglobin, an obvious pink colour (judged by visual inspection) and a significantly higher a-value than the control samples or samples inoculated with P. pentosaceus. In raw meat batters, the a-values of the S. xylosus samples were almost the same as those for the meat with nitrite added. The complementary analysis of meat batter samples by photochemical information from UV-vis, electron spin resonance and resonance Raman spectroscopy revealed that the existing status of the myoglobin in meat batters inoculated with S. xylosus was mainly pentacoordinate nitrosylmyoglobin. This study provides a potential solution for nitrite substitute in meat products.

Sodium nitrite: the "cure" for nitric oxide insufficiency

This process of "curing" food is a long practice that dates back thousands of years long before refrigeration or food safety regulations. Today food safety and mass manufacturing are dependent upon safe and effective means to cure and preserve foods including meats. Nitrite remains the most effective curing agent to prevent food spoilage and bacterial contamination. Despite decades of rigorous research on its safety and efficacy as a curing agent, it is still regarded by many as a toxic undesirable food additive. However, research within the biomedical science community has revealed enormous therapeutic benefits of nitrite that is currently being developed as novel therapies for conditions associated with nitric oxide (NO) insufficiency. Much of the same biochemistry that has been understood for decades in the meat industry has been rediscovered in human physiology. This review will highlight the fundamental biochemistry of nitrite in human physiology and highlight the risk benefit evaluation surrounding nitrite in food and meat products. Foods or diets enriched with nitrite can have profound positive health benefits.

Ferrochelatase catalyzes the formation of Zn-protoporphyrin of dry-cured ham via the conversion reaction from heme in meat

Ferrochelatase (FECH), the enzyme at the last step of the heme-biosynthetic pathway, is involved in the formation of Zn-protoporphyrin via an iron-removal reaction of heme. To improve the efficacy of the formation of Zn-protoporphyrin from heme, the use of recombinant FECHs from porcine, yeast, and bacteria was examined. Incubation of FECH with myoglobin in the presence of ascorbic acid and cysteine resulted in the efficient conversion of myoglobin-heme to Zn-protoporphyrin. Exogenously added recombinant yeast FECH facilitates the production of Zn-protoporphyrin from myoglobin-heme and heme in meat, via the replacement of iron in the protoporphyrin ring by zinc ions. A large amount of Zn-protoporphyrin was also generated by the catalysis of FECH using an intact piece of meat as a substrate. These findings can open up possible approaches for the generation of a nontoxic bright pigment, Zn-protoporphyrin, to shorten the incubation time required to produce dry-cured ham.

Photofunctional multilayer films by assembling naked silver nanoparticles and a tailored nitric oxide photodispenser at water/air interface

This contribution reports the design, preparation, and characterization of nanostructured hybrid films of silver nanoparticles (AgNPs) and a tailored nitric oxide (NO) photodonor. They were achieved by exploiting effective interfacial interactions between an amino-terminated NO photodonor spread onto water surface and naked AgNPs dissolved in the water subphase. The morphology, the spectroscopic features, and the interaction between the two components in the floating films at the air/water interface were inspected by Brewster Angle Microscopy, UV-Vis reflection, and polarization-modulation infrared reflection-absorption spectroscopy. AgNPs and the NO photodonor were successfully transferred onto hydrophobized quartz substrates by horizontal lifting deposition and the resulting multilayer films were characterized by UV-Vis absorption spectroscopy and transmission electron microscopy, respectively. The results obtained showed the presence of both isolated AgNPs and assemblies of AgNPs having nanodimensional character in the films. The photochemical properties of the NO photodonor were well preserved in the hybrid multilayers. In fact, they were able to release NO under visible light excitation, as unambiguously demonstrated by the direct and in real-time monitoring of this transient species using an ultrasensitive electrode, and the transfer of the released NO to a protein such as myoglobin.