Nitric oxide and myoglobins

S-nitrosoproteomics profiling elucidates the regulatory mechanism of S-nitrosylation on beef quality

This study aimed to quantitively profile the S-nitrosylation in beef semimembranosus (SM) with different treatments (nitric oxide donor or nitric oxide synthase inhibitor) by applying iodoTMT-based nitrosoproteomics. Results showed that 2096 S-nitrosylated cysteine sites in 368 proteins were detected in beef SM. Besides, differential SNO-modified proteins were screened, some of which were involved in crucial biochemical pathways, including calcium-releasing-related proteins, energy metabolic enzymes, myofibrils, and cytoskeletal proteins. GO analysis indicated that differential proteins were localized in a wide range of cellular compartments, such as cytoplasm, organelle, and mitochondrion, providing a prerequisite for S-nitrosylation exerting broad roles in post-mortem muscles. Furthermore, KEGG analysis validated that these proteins participated in the regulation of diverse post-mortem metabolic processes, especially glycolysis. To conclude, changes of S-nitrosylation levels in post-mortem muscles could impact the structure and function of crucial muscle proteins, which lead to different levels of muscle metabolism and ultimately affect beef quality.

A versatile delivery vehicle for cellular oxygen and fuels or metabolic sensor? A review and perspective on the functions of myoglobin

A canonical view of the primary physiological function of myoglobin (Mb) is that it is an oxygen (O2) storage protein supporting mitochondrial oxidative phosphorylation, especially as the tissue O2 partial pressure (Po2) drops and Mb off-loads O2. Besides O2 storage/transport, recent findings support functions for Mb in lipid trafficking and sequestration, interacting with cellular glycolytic metabolites such as lactate (LAC) and pyruvate (PYR), and "ectopic" expression in some types of cancer cells and in brown adipose tissue (BAT). Data from Mb knockout (Mb-/-) mice and biochemical models suggest additional metabolic roles for Mb, especially regulation of nitric oxide (NO) pools, modulation of BAT bioenergetics, thermogenesis, and lipid storage phenotypes. From these and other findings in the literature over many decades, Mb's function is not confined to delivering O2 in support of oxidative phosphorylation but may serve as an O2 sensor that modulates intracellular Po2- and NO-responsive molecular signaling pathways. This paradigm reflects a fundamental change in how oxidative metabolism and cell regulation are viewed in Mb-expressing cells such as skeletal muscle, heart, brown adipocytes, and select cancer cells. Here, we review historic and emerging views related to the physiological roles for Mb and present working models illustrating the possible importance of interactions between Mb, gases, and small-molecule metabolites in regulation of cell signaling and bioenergetics.

Lipid Peroxidation in Muscle Foods: Impact on Quality, Safety and Human Health

The issue of lipid changes in muscle foods under the action of atmospheric oxygen has captured the attention of researchers for over a century. Lipid oxidative processes initiate during the slaughtering of animals and persist throughout subsequent technological processing and storage of the finished product. The oxidation of lipids in muscle foods is a phenomenon extensively deliberated in the scientific community, acknowledged as one of the pivotal factors affecting their quality, safety, and human health. This review delves into the nature of lipid oxidation in muscle foods, highlighting mechanisms of free radical initiation and the propagation of oxidative processes. Special attention is given to the natural antioxidant protective system and dietary factors influencing the stability of muscle lipids. The review traces mechanisms inhibiting oxidative processes, exploring how changes in lipid oxidative substrates, prooxidant activity, and the antioxidant protective system play a role. A critical review of the oxidative stability and safety of meat products is provided. The impact of oxidative processes on the quality of muscle foods, including flavour, aroma, taste, colour, and texture, is scrutinised. Additionally, the review monitors the effect of oxidised muscle foods on human health, particularly in relation to the autooxidation of cholesterol. Associations with coronary cardiovascular disease, brain stroke, and carcinogenesis linked to oxidative stress, and various infections are discussed. Further studies are also needed to formulate appropriate technological solutions to reduce the risk of chemical hazards caused by the initiation and development of lipid peroxidation processes in muscle foods.

Study of the Oxidative and Microbiological Stability of Nitrite-Reduced, Vacuum-Packed, Refrigerated Lamb Sausages Supplemented with Red Propolis Extract

Vacuum-packed lamb sausages with or without red propolis extract and a reduced sodium nitrite content were evaluated for oxidative and microbiological stability during storage for 21 days at 2 °C. The following treatments were evaluated: EN150 (control, base formulation (BF) + 500 mg/kg sodium erythorbate and 150 mg/kg sodium nitrite); EN75 (BF + 500 mg/kg sodium erythorbate and 75 mg/kg sodium nitrite); P1N75 (without the addition of erythorbate, BF + 1800 mg/kg propolis extract and 75 mg/kg sodium nitrite); and P2N75 (without the addition of erythorbate, BF + 3600 mg/kg propolis extract and 75 mg/kg sodium nitrite). Analyses were conducted to characterize the samples on day 0 with respect to the proximate composition (moisture, protein, fat, and ash) and sensory acceptance. Stability during refrigerated storage was evaluated on days 0, 7, 14 and 21 for the parameters pH, color profile (L*, a*, and b*), TBARs index (oxidative stability) and microbiological count of aerobic psychrotrophic microorganisms. Texture profile, cooking weight loss (WLC), peroxide index and free fatty acids were evaluated on days 0 and 21. The treatments with propolis and reduced nitrite (EN150 and P1N75) showed a red color intensity (a*) similar to the treatment with erythorbate and the same nitrite content (EN75) at the end of storage, maintaining the characteristic reddish color of the sausages. The extract slowed down lipid oxidation during storage, especially P2N75, which showed the lowest level of TBARS (0.39 mg MDA/kg) and the peroxide index (2.13 mEq g O2) on day 21. The residual nitrite value in EN75 was the lowest (p < 0.05) on day 21, showing that synthetic antioxidants are more efficient than the extract in nitrite reduction reactions. The results for the counts of psychrotrophic microorganisms showed that the extract did not have the expected antimicrobial effect on the growth of this microorganisms, and leveling the results revealed no differences (p < 0.05) between the treatments. Despite the red propolis extract not showing a significant antimicrobial improvement in lamb sausages, it can be considered a healthy option with good prospects for replacing synthetic antioxidants with a natural product.

Exploring second coordination sphere effects in flavodiiron nitric oxide reductase model complexes

Flavodiiron nitric oxide reductases (FNORs) equip pathogens with resistance to nitric oxide (NO), an important immune defense agent in mammals, allowing these pathogens to proliferate in the human body, potentially causing chronic infections. Understanding the mechanism of how FNORs mediate the reduction of NO contributes to the greater goal of developing new therapeutic approaches against drug-resistant strains. Recent density functional theory calculations suggest that a second coordination sphere (SCS) tyrosine residue provides a hydrogen bond that is critical for the reduction of NO to N2O at the active site of FNORs [J. Lu, B. Bi, W. Lai and H. Chen, Origin of Nitric Oxide Reduction Activity in Flavo-Diiron NO Reductase: Key Roles of the Second Coordination Sphere, Angew. Chem., Int. Ed., 2019, 58, 3795-3799]. Specifically, this H-bond stabilizes the hyponitrite intermediate and reduces the energetic barrier for the N-N coupling step. At the same time, the role of the Fe⋯Fe distance and its effect on the N-N coupling step has not been fully investigated. In this study, we equipped the H[BPMP] (= 2,6-bis[[bis(2-pyridylmethyl)amino]methyl]-4-methylphenol) ligand with SCS amide groups and investigated the corresponding diiron complexes with 0-2 bridging acetate ligands. These amide groups can form hydrogen bonds with the bridging acetate ligand(s) and potentially the coordinated NO groups in these model complexes. At the same time, by changing the number of bridging acetate ligands, we can systematically vary the Fe⋯Fe distance. The reactivity of these complexes with NO was then investigated, and the formation of stable iron(II)-NO complexes was observed. Upon one-electron reduction, these NO complexes form Dinitrosyl Iron Complexes (DNICs), which were further characterized using IR and EPR spectroscopy.

Impact of nitrite-embedded packaging film on quality and sensory attributes of alternatively-cured and nitrite-free bologna

The objectives were to determine the effects of post-thermal processing nitrite-embedded film (NEF) packaging on the quality attributes of alternatively-cured (nitrite from celery juice powder (AC)) and nitrite-free bologna. Attributes evaluated included lipid oxidation, instrumental color, pigment concentration, and sensory properties such as cured meat flavor, aroma, and color. Three bologna formulations, each packaged with two packaging films were produced. A conventionally-cured control formulation (with nitrite from sodium nitrite; CON), a nitrite-free formulation (UCC), and an alternatively cured formulation (nitrite from cultured celery juice powder; AC) were packaged in conventional (CF) or nitrite-embedded (NEF) film. Instrumental a* values (measured during both light and dark storage at intervals of 7 or 14 days over 126 days of storage) and cured pigment concentration (measured at 14-day intervals over 84 days of storage) were significantly greater (P < 0.05) for the UCC-NEF treatment compared to its conventional film counterpart, UCC-CF. No significant differences (P > 0.05) for lipid oxidation (TBARS values) were observed with NEF. Trained sensory panelists, who evaluated samples at 14-day intervals over 70 days of storage, found significantly greater (P < 0.05) cured aroma, cured flavor, pink color and less off-flavor for uncured bologna packaged in NEF compared to conventional film. For the uncured bologna formulation, NEF packaging provided cured meat attributes comparable to the control formulation that included nitrite. This is the first time that cured aroma and flavor have been observed when nitrite from packaging film is added to a cooked meat product under anaerobic conditions.

Meat color and iridescence: Origin, analysis, and approaches to modulation

Meat color is an important aspect for the meat industry since it strongly determines the consumers' perception of product quality and thereby significantly influences the purchase decision. Emergence of new vegan meat analogs has renewed interest in the fundamental aspects of meat color in order to replicate it. The appearance of meat is based on a complex interplay between the pigment-based meat color from myoglobin and its chemical forms and light scattering from the muscle's microstructure. While myoglobin biochemistry and pigment-based meat color have been extensively studied, research on the physicochemical contribution of light scattering to meat color and the special case of structural colors causing meat iridescence has received only little attention. Former review articles focused mostly on the biochemical or physical mechanisms rather than the interplay between them, in particular the role that structural colors play. While from an economic point of view, meat iridescence might be considered negligible, an enhanced understanding of the underlying mechanisms and the interactions of light with meat microstructures can improve our overall understanding of meat color. Therefore, this review discusses both biochemical and physicochemical aspects of meat color including the origin of structural colors, highlights new color measurement methodologies suitable to investigate color phenomena such as meat iridescence, and finally presents approaches to modulate meat color in terms of base composition, additives, and processing.

The mechanism of Leuconostoc mesenteroides subsp. IMAU:80679 in improving meat color: Myoglobin oxidation inhibition and myoglobin derivatives formation based on multi enzyme-like activities

The Leuconostoc mesenteroides subsp. IMAU:80679 (LM) was chosen for its superior capability in enhancing redness, and was incubated in a broth system containing metmyoglobin (MetMb) to investigate its mechanisms for color improvement. The a* value of LM group reached its highest level of 52.75 ± 1.04 at 24 h, significantly higher than control of 19.75 ± 0.6 (p < 0.05). The addition of LM could inhibit myoglobin oxidation to some extent. Meanwhile, higher content of nitrosylmyoglobin (NOMb) and Zn-protoporphyrin (Znpp) were observed in LM samples during the whole incubation period. Furthermore, enzymatic activity and encoded genes related to MetMb reduction and pigment formation were determined to explain its possible mechanism on color enhancement. Finally, by extracting crude enzymes and adding them to meat batters, the redness of crude enzyme group was comparable to that achieved with 20 ppm nitrite, providing a potential method on compensating for nitrite/nitrate substitution in meat products.

Bacterial nitric oxide synthase in colorizing meat products: Current development and future directions

Nitrite has been widely used in meat products for its abilities including color formation, antimicrobial properties, flavor formation and preventing lipid oxidation. However, the possible generation of N-nitrosamines through reaction of nitrite with secondary amines arises many concerns in the usage of nitrite. For a long time, nitrite substitution is unsettled issue in the meat industry. Many attempts have been tried, however, the alternative solutions are often ephemeral and palliative. In recent years, bacterial nitric oxide synthase (bNOS) has received attention for its critical roles, especially in reddening meat products. This comprehensive background study summarizes the application of bNOS in colorizing meat products, its functions in bacteria, and methods of regulating the bNOS pathway. Based on this information, some strategies for promoting the nitric oxide yield for effectively substituting nitrite are presented, such as changing the environmental conditions for bacterial survival and adding substrate. Thus, bNOS is a promising nitrite substitute for color formation, and further research on its other roles in meat needs to be carried out to obtain the complete picture.

Myoglobin-Pyruvate Interactions: Binding Thermodynamics, Structure-Function Relationships, and Impact on Oxygen Release Kinetics

Myoglobin (Mb), besides its roles as an oxygen (O₂) carrier/storage protein and nitric oxide NO scavenger/producer, may participate in lipid trafficking and metabolite binding. Our recent findings have shown that O₂ is released from oxy-Mb upon interaction with lactate (LAC, anerobic glycolysis end-product). Since pyruvate (PYR) is structurally similar and metabolically related to LAC, we investigated the effects of PYR (aerobic glycolysis end-product) on Mb using isothermal titration calorimetry, circular dichroism, and O₂-kinetic studies to evaluate PYR affinity toward Mb and to compare the effects of PYR and LAC on O₂ release kinetics of oxy-Mb. Similar to LAC, PYR interacts with both oxy- and deoxy-Mb with a 1:1 stoichiometry. Time-resolved circular dichroism spectra revealed that there are no major conformational changes in the secondary structures of oxy- or deoxy-Mb during interactions with PYR or LAC. However, we found contrasting results with respect to binding affinities and substrate preference, where PYR has higher affinity toward deoxy-Mb when compared with LAC (which prefers oxy-Mb). Furthermore, PYR interaction with oxy-Mb releases a significantly lower amount of O₂ than LAC. Taken together, our findings support the hypothesis that glycolytic end-products play a distinctive role in the Mb-rich tissues by serving as novel regulators of O₂ availability, and/or by impacting other activities related to oxy-/deoxy-Mb toggling in resting vs. exercised or metabolically activated conditions.

Effects of nitric oxide synthase inhibitor on mitochondria apoptosis and meat quality in postmortem Gannan yak (Bos grunniens) meat

This research aimed to explore the effects of the nitric oxide synthase (NOS) inhibitor (L-NAME) on mitochondria apoptosis in postmortem Gannan yak (Bos grunniens) longissimus dorsi (LD) muscle and to explore its effect on meat quality further. The Gannan yak meat samples were treated with the control group (0.9% NaCl) and L-NAME (20, 60, and 100 mM) for 24 h and then stored for 0, 1, 3, 5, and 7 days at 4°C. NOS activity and NO content were investigated, and the parameters of mitochondrial apoptosis of the postmortem Gannan yak meat were determined. Meanwhile, the meat quality such as the centrifugation loss, meat color, and myofibril fragmentation index (MFI) was evaluated. The results indicated that after treatment with L-NAME, NOS activity and NO content decreased, causing mitochondrial membrane damage, Bax protein, and Cyt-c levels increased, and resulted in increased activities of caspase-9 and -3, promoting the occurrence of mitochondrial apoptosis. Furthermore, it increased the tenderness and water retention of Gannan yak meat. The results indicated that NOS inhibitor played a regulatory role in postmortem Gannan yak meat quality by regulating mitochondria apoptosis during postmortem aging. PRACTICAL APPLICATIONS: The meat's tenderness is often considered the most important factor affecting consumers' willingness to repurchase. The relationship of caspases and MFI suggested that L-NAME played a regulatory role in postmortem Gannan yak meat quality by regulating mitochondria apoptosis during postmortem aging. This study provides valuable information for the development of the Gannan yak economy in Tibetan areas.

Bioinorganic Chemistry on Electrodes: Methods to Functional Modeling

One of the major goals of bioinorganic chemistry has been to mimic the function of elegant metalloenzymes. Such functional modeling has been difficult to attain in solution, in particular, for reactions that require multiple protons and multiple electrons (nH⁺/ne^-). Using a combination of heterogeneous electrochemistry, electrode and molecule design one may control both electron transfer (ET) and proton transfer (PT) of these nH⁺/ne^- reactions. Such control can allow functional modeling of hydrogenases (H⁺ + e^- → 1/2 H₂), cytochrome c oxidase (O₂ + 4 e^- + 4 H⁺ → 2 H₂O), monooxygenases (RR'CH₂ + O₂ + 2 e^- + 2 H⁺ → RR'CHOH + H₂O) and dioxygenases (S + O₂ → SO₂; S = organic substrate) in aqueous medium and at room temperatures. In addition, these heterogeneous constructs allow probing unnatural bioinspired reactions and estimation of the inner- and outer-sphere reorganization energy of small molecules and proteins.

Myoglobin Interaction with Lactate Rapidly Releases Oxygen: Studies on Binding Thermodynamics, Spectroscopy, and Oxygen Kinetics

Myoglobin (Mb)-mediated oxygen (O₂) delivery and dissolved O₂ in the cytosol are two major sources that support oxidative phosphorylation. During intense exercise, lactate (LAC) production is elevated in skeletal muscles as a consequence of insufficient intracellular O₂ supply. The latter results in diminished mitochondrial oxidative metabolism and an increased reliance on nonoxidative pathways to generate ATP. Whether or not metabolites from these pathways impact Mb-O₂ associations remains to be established. In the present study, we employed isothermal titration calorimetry, O₂ kinetic studies, and UV-Vis spectroscopy to evaluate the LAC affinity toward Mb (oxy- and deoxy-Mb) and the effect of LAC on O₂ release from oxy-Mb in varying pH conditions (pH 6.0–7.0). Our results show that LAC avidly binds to both oxy- and deoxy-Mb (only at acidic pH for the latter). Similarly, in the presence of LAC, increased release of O₂ from oxy-Mb was detected. This suggests that with LAC binding to Mb, the structural conformation of the protein (near the heme center) might be altered, which concomitantly triggers the release of O₂. Taken together, these novel findings support a mechanism where LAC acts as a regulator of O₂ management in Mb-rich tissues and/or influences the putative signaling roles for oxy- and deoxy-Mb, especially under conditions of LAC accumulation and lactic acidosis.

Second Sphere Effects on Oxygen Reduction and Peroxide Activation by Mononuclear Iron Porphyrins and Related Systems

Activation and reduction of O₂ and H₂O₂ by synthetic and biosynthetic iron porphyrin models have proved to be a versatile platform for evaluating second-sphere effects deemed important in naturally occurring heme active sites. Advances in synthetic techniques have made it possible to install different functional groups around the porphyrin ligand, recreating artificial analogues of the proximal and distal sites encountered in the heme proteins. Using judicious choices of these substituents, several of the elegant second-sphere effects that are proposed to be important in the reactivity of key heme proteins have been evaluated under controlled environments, adding fundamental insight into the roles played by these weak interactions in nature. This review presents a detailed description of these efforts and how these have not only demystified these second-sphere effects but also how the knowledge obtained resulted in functional mimics of these heme enzymes.

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

Thermoplastic starch blown films functionalized by plasticized nitrite blended with PBAT for superior oxygen barrier and active biodegradable meat packaging

Functional bioplastic packaging was produced from thermoplastic starch (TPS) with nitrite (1-5%) and polybutylene adipate terephthalate (PBAT) (PBAT/TPS at 30/70 and 40/60) via blown-film extrusion. TPS-nitrite interaction increased thermal destabilization and decreased α-relaxation temperature of TPS phase, indicating improved plasticization and disruption of starch granules. Nitrite modified C=O bonding of PBAT and improved compatibility with TPS networks, resulting in compact microstructures that reduced oxygen and water vapor permeability. Films containing nitrite showed up to 39.7% decrease (p≤0.05) in mechanical properties while effectively improving and stabilizing redness of vacuum-packaged pork during storage for 12 days. Nitrite release led to up to 0.66 ppm residual nitrite, which corresponded to formation of nitrosyl myoglobin (3.4-9.6 ppm), and effectively reduced total viable count, lactic acid bacteria and yeast and molds (p≤0.05). Stabilized lipid components also increased with increasing nitrite. Novel nitrite-containing biodegradable film enhanced functional properties and retained quality of packaged meat.

High ZnPP-forming food-grade lactic acid bacteria as a potential substitute for nitrite/nitrate to improve the color of meat products

Zinc protoporphyrin IX (ZnPP)-forming food-grade lactic acid bacteria (LAB) were screened from various sources for their ability to improve the color of meat products. The effects of salt and nitrite on the ZnPP-forming ability of these bacteria were also investigated. Finally, these bacteria were applied in salt-added minced meat to assess their ability to improve the color. Twenty-five LAB were screened for their ZnPP-forming ability in pork. Most of the strains exhibited maximum growth anaerobically in 3% salt at 30 °C and grew well at pH 5.5 and 6.5. Moreover, 3% salt slightly retarded ZnPP formation; however, nitrite completely inhibited ZnPP formation in all the ZnPP-forming LAB. Thirteen LAB (avoiding duplication and non-food-grade) could form ZnPP in salt-added minced meat, resulting in improvement of the bright red color, high ZnPP autofluorescence, and increased fluorescence intensity. Finally, considering the safety, Lactobacillus plantarum, Lactococcus lactis subsp. cremoris, and Leuconostoc lactis were suggested as promising candidates to improve the color of meat products.

A facile dual-function fluorescent probe for detection of phosgene and nitrite and its applications in portable chemosensor analysis and food analysis

Due to the potential threats of phosgene and nitrite to public health and safety, in this work, we first proposed the application of a facile dual-function fluorescent probe 2-(1H-Benzimidazol-2-yl)Aniline (BMA) for the detection of phosgene and nitrite in different solvent environments. BMA had fast response (1 min), high selectivity and sensitivity (the limit of detection was 1.27 nM) to phosgene in CH₃CN solution (containing 10% DMSO), which manifested as a ratiometric fluorescent mode from 416 nm to 480 nm. The response of BMA to nitrite in HCl solution (pH = 1, containing 10% CH₃CN) was also highly selective and sensitive (the limit of detection was 60.63 nM), which shown as a turn-off fluorescent mode at 485 nm. In addition, two portable chemosensors (BMA-loaded TLC plates and test strips) had also been successfully manufactured for the detection of phosgene in the gas phase and nitrite in solution, which displayed good responses. Most importantly, BMA had also been successfully used for detection of nitrite in food samples, and a good recovery (88.5%-107.2%) was obtained by adding standard sodium nitrite.

Effects of nitrite incorporated active films on quality of pork

Nitrite (0.25-2%) incorporated thermoplastic starch (TPS) and linear low-density polyethylene (LLDPE) blend films were produced by the conventional blown-film extrusion process. Films were characterized and determined for efficacy as active packaging for pork steak. Scanning electron micrographs showed enhanced starch granule disruption due to melting. Increased nitrite contents enhanced the starch network and improved mechanical properties. Water vapor and barrier properties of blend films were improved by nitrite incorporation, with increased compatibility between TPS and LLDPE networks. Films containing 0.5% nitrite effectively improved redness and corresponded to 0.06 ppm residual nitrite and 75 ppm nitrosomyoglobin in packaged pork. Nitrite addition modified protein secondary conformation involving CO stretching bonds via H-bonding, while films with 1% and 2% nitrite significantly inhibited growth of lactic acid bacteria, yeast and mold, and retained softer texture during storage. Nitrite incorporated films were demonstrated as efficient active packaging to improve the quality of red meat products.

Reactivity and degradation products of tryptophan in solution and proteins

Tryptophan is one of the essential mammalian amino acids and is thus a required component in human nutrition, animal feeds, and cell culture media. However, this aromatic amino acid is highly susceptible to oxidation and is known to degrade into multiple products during manufacturing, storage, and processing. Many physical and chemical processes contribute to the degradation of this compound, primarily via oxidation or cleavage of the highly reactive indole ring. The central contributing factors are reactive oxygen species, such as singlet oxygen, hydrogen peroxide, and hydroxyl radicals; light and photosensitizers; metals; and heat. In a multi-component mixture, tryptophan also commonly reacts with carbonyl-containing compounds, leading to a wide variety of products. The purpose of this review is to summarize the current state of knowledge regarding the degradation and interaction products of tryptophan in complex liquid solutions and in proteins. For the purposes of context, a brief summary of the key pathways in tryptophan metabolism will be included, along with common methods and issues in tryptophan manufacturing. The review will focus on the conditions that lead to tryptophan degradation, the products generated in these processes, their known biological effects, and methods which may be applied to stabilize the amino acid.

A Single Iron Porphyrin Shows pH Dependent Switch between "Push" and "Pull" Effects in Electrochemical Oxygen Reduction

The "push-pull" effects associated with heme enzymes manifest themselves through highly evolved distal amino acid environments and axial ligands to the heme. These conserved residues enhance their reactivities by orders of magnitude relative to small molecules that mimic the primary coordination. An instance of a mononuclear iron porphyrin with covalently attached pendent phenanthroline groups is reported which exhibit reactivity indicating a pH dependent "push" to "pull" transition in the same molecule. The pendant phenanthroline residues provide proton transfer pathways into the iron site, ensuring selective 4e^-/4H⁺ reduction of O₂ to water. The protonation of these residues at lower pH mimics the pull effect of peroxidases, and a coordination of an axial hydroxide ligand at high pH emulates the push effect of P450 monooxygenases. Both effects enhance the rate of O₂ reduction by orders of magnitude over its value at neutral pH while maintaining exclusive selectivity for 4e^-/4H⁺ oxygen reduction reaction.

Phenosafranin-Based Colorimetric-Sensing Platform for Nitrite Detection Enabled by Griess Assay

A facile and effective colorimetric-sensing platform based on the diazotization of phenosafranin for the detection of NO 2 - under acidic conditions using the Griess assay is presented. Diazotization of commercial phenosafranin produces a color change from purplish to blue, which enables colorimetric quantitative detection of NO 2 - . Optimal detection conditions were obtained at a phenosafranin concentration of 0.25 mM, HCl concentration of 0.4 M, and reaction time of 20 min. Under the optimized detection conditions, an excellent linearity range from 0 to 20 μM was obtained with a detection limit of 0.22 μM. Favorable reproducibility and selectivity of the colorimetric sensing platform toward NO 2 - were also verified. In addition, testing spiked ham sausage, bacon, and sprouts samples demonstrated its excellent practicability. The presented colorimetric sensing platform is a promising candidate for the detection of NO 2 - in real applications.

Fluorescent recognition and selective detection of nitrite ions with carbon quantum dots

The nitrite ion (NO₂^-) is a vital inorganic species that occurs both in natural ecological systems and human bodies. The high concentration of NO₂^- can be harmful for animal and human health. It is important to develop a simple, sensitive, reliable, and economic methodology to precisely monitor NO₂^- in various environmental and biological fields. Thus, a novel nitrite biosensor based on carbon quantum dots (PA-CDs) has been constructed and prepared via a high-efficiency, one-pot hydrothermal route using primary arylamines (PA) such as m-phenylenediamine. The device exhibits bright green fluorescence and a high quantum yield of 20.1% in water. In addition, the PA-CDs also possess two broad linear ranges: 0.05-1.0 μM and 1.0-50 μM with a low detection limit of 7.1 nM. The classical diazo reaction is firstly integrated into the PA-CD system by primary arylamines, which endows the system with high sensitivity and specific selectivity towards nitrite. Importantly, the nanosensor can detect NO₂^- in environmental water and serum samples with high fluorescence recoveries, demonstrating its feasibility in practical applications. This work broadens a new method to fabricate novel nanosensors and provides a prospective application for fluorescent carbon quantum dots (CDs). Graphical abstract.

Theoretical basis of nitrosomyoglobin formation in a dry sausage model by coagulase-negative staphylococci: Behavior and expression of nitric oxide synthase

Three coagulase-negative staphylococci (CNS) species were investigated for gene expression of nitric oxide synthase (NOS) and the ability of nitrosomyoglobin (NO-Mb) formation in a dry sausage model without nitrite addition. The expression of nos gene was systematically proven from DNA to RNA to protein, and nitric oxide (NO) generation was also directly detected. In the dry sausage model system, the redness (a*-values) of samples inoculated with the three CNS species were higher than those inoculated with Pediococcus pentosaceus and the control (P < 0.05). The results from UV-vis and electron spin resonance spectroscopies revealed that pentacoordinate NO-Mb was formed in the sausages with either CNS or nitrite added. The sausage inoculated with Staphylococcus vitulinus had the highest NO-Mb content among the CNS-treated sausages. Dimer interface residues and phosphorylation sites of NOS in . itulinus differ from the other two CNS species as revealed by amino acid sequences, which may be responsible for the different catalytic activities.

Quality properties of sausage incorporated with flaxseed and tomato powders

The present study investigates the chemical properties and sensory attributes of beef sausages which have been incorporated with three tomato powder levels (0, 1.5 and 3%) and three flaxseed powder levels (0, 3 and 6%). All samples were stored at 4 °C for 42 days. The addition of tomato and flaxseed powders decreased (P < .001) L* values, pH, residual nitrite and moisture contents and increased b* value (P < .001), protein, carbohydrate, ash, fiber and total calories contents. The nitrite content decreased during the storage time. Linolenic acid increased with the addition of flaxseed powder. Generally, adding tomato and flaxseed powders up to 3% had no effect (P > .05) on the sensory evaluation parameters on cooked and fried sausages. Based on the obtained results, it is possible to produce sausages incorporated with tomato and flaxseed powders and introduce to the market as a new processed meat product.

The Impact of Residual O2, Temperature, and Light at Display on Sensory Attributes of Sliced, Packaged Salami

The aim of the study was to examine if small amounts of oxygen (O2) causing discolouration of salami exposed to light in the grocery store also cause adverse changes in the flavour and odour sensory profile. Sensory properties of packaged sliced salami under different temperatures (4, 20°C, and 23°C), two lights sources (LED and fluorescent), and a low level of residual O2 in the headspace were evaluated. The experiment consisted of nine series, which were sensory-assessed after 3 and 6 days of display. A combination of light exposure and residual O2 causing discolouration resulted in substantial off-flavour and off-odour of the displayed salami, both on the upper slice exposed to light and the middle slice in the stack with no direct light exposure. Samples from all other series without O2 and those displayed in various light or stored in darkness showed no changes in quality compared with control samples stored in darkness. Temperature at display did not affect sensory attributes in the series without O2 in the headspace. Sensory results from 3 to 6 days display were similar. To minimize quality defects and food waste, producers and retailers are advised to store packages of sliced salami in darkness until nearly all residual O2 is consumed internally by the product before placing the packages upon light in the counter.

Resonance Raman Spectroscopy and Density Functional Theory Calculations on Ferrous Porphyrin Dioxygen Adducts with Different Axial Ligands: Correlation of Ground State Wave Function and Geometric Parameters with Experimental Vibrational Frequencies

A dioxygen adduct of ferrous porphyrin is an important chemical species in nature as it is a common intermediate in all oxygen transfer, storage, reducing, and activating heme enzymes. The ground state (GS) wave function of this complex has been investigated using several techniques like resonance Raman (rR), Mossbauer, and X-ray absorption spectroscopies. The Fe-O and O-O vibrations of these six-coordinated diamagnetic species show a positive correlation with each other in contrast to analogous ferrous carbonyl complexes where the Fe-CO vibration correlates negatively with the C-O vibration due to a synergistic effect. In this Article, three Fe-porphyrins with different axial ligands (imidazole, phenolate, and thiolate) are investigated using rR spectroscopy and density functional theory (DFT) calculations. The GS wave functions of these species are analyzed, and the contribution of the three primary bonding interactions in the Fe-O₂ unit (a σ interaction from the in-plane π* of the superoxide to the vacant d_z² of Fe, a π donation from the out of plane (oop) π* to the d_π orbital of Fe, and a π back bonding interaction from the d_π orbital of Fe to the oop π* of the superoxide) to the calculated Fe-O and O-O vibrations and bond lengths are deconvoluted using a MO theory framework. The GS wave function provides a basis for the correlations observed between different vibrational and geometric parameters of these dioxygen adducts. Furthermore, the correlations obtained allows estimation of the GS wave function and geometry of these species (both natural and artificial) using their experimentally observed Fe-O/O-O vibrations. The wave functions thus extracted from the experimental vibrational data reported offer insight into the role of the axial ligand and hydrogen bonding on the geometric and electronic structures of these crucial chemical species in different protein active sites.

l-Lysine/l-arginine/l-cysteine synergistically improves the color of cured sausage with NaNO2 by hindering myoglobin oxidation and promoting nitrosylmyoglobin formation

This study aimed to evaluate the effects of l-lysine (Lys)/l-arginine (Arg)/l-cysteine (Cys) on the color of cured sausage and the possible mechanism underlying these effects. The results indicated that the combined addition of Arg/Lys/Cys and NaNO₂ effectively increased the a* values and nitroso pigment content but decreased the MetMb(Fe³⁺) content in cured sausage, compared with the individual addition of Arg/Lys/Cys and NaNO₂. The cured sausage treated with combined Arg/Lys/Cys and NaNO₂ contained significantly lower residual nitrite than those treated with only NaNO₂. UV-vis spectroscopy and electron paramagnetic resonance spectroscopy revealed that pentacoordinate nitrosyl ferrohemochrome was the main pigment component in the cured sausage treated with NaNO₂ or combined Arg/Lys/Cys and NaNO₂ and higher content in the latter one. The results suggest that Arg/Lys/Cys hindered myoglobin oxidation and promoted pentacoordinate nitrosylmyoglobin formation, which could contribute to the improved color of cured sausage. The results are of interest in the meat industry.

Hydrogen atom abstraction by synthetic heme ferric superoxide and hydroperoxide species

To date, artificial dioxygen adducts of heme have not been demonstrated to be able to oxidize organic substrates in sharp contrast to their non-heme analogues and naturally occurring enzymes like heme dioxygenases. To address this apparent anomaly, an iron porphyrin complex is synthesized which includes a pendant quinol group. The corresponding dioxygen bound iron porphyrin species is demonstrated to perform hydrogen atom transfer (HAT) from the quinol group appended to the porphyrin ligand. The resultant ferric peroxide, formed by the first HAT, performs a 2nd HAT generating a ferryl species (FeIV[double bond, length as m-dash]O) and resulting in the 2e-/2H+ oxidation of the pendant hydroquinone to quinone.

Effect of hydrogen bonding on innocent and non-innocent axial ligands bound to iron porphyrins

Most known heme enzymes utilize hydrogen bonding interactions in their active sites to control electronic and geometric structures and the ensuing reactivity.

Nitrosyl Myoglobins and Their Nitrite Precursors: Crystal Structural and Quantum Mechanics and Molecular Mechanics Theoretical Investigations of Preferred Fe -NO Ligand Orientations in Myoglobin Distal Pockets

The globular dioxygen binding heme protein myoglobin (Mb) is present in several species. Its interactions with the simple nitrogen oxides, namely, nitric oxide (NO) and nitrite, have been known for decades, but the physiological relevance has only recently become more fully appreciated. We previously reported the O-nitrito mode of binding of nitrite to ferric horse heart wild-type (wt) MbIII and human hemoglobin. We have expanded on this work and report the interactions of nitrite with wt sperm whale (sw) MbIII and its H64A, H64Q, and V68A/I107Y mutants whose dissociation constants increase in the following order: H64Q < wt < V68A/I107Y < H64A. We also report their X-ray crystal structures that reveal the O-nitrito mode of binding of nitrite to these derivatives. The MbII-mediated reductions of nitrite to NO and structural data for the wt and mutant MbII-NOs are described. We show that their FeNO orientations vary with distal pocket identity, with the FeNO moieties pointing toward the hydrophobic interiors when the His64 residue is present but toward the hydrophilic exterior when this His64 residue is absent in this set of mutants. This correlates with the nature of H-bonding to the bound NO ligand (nitrosyl O vs N atom). Quantum mechanics and hybrid quantum mechanics and molecular mechanics calculations help elucidate the origin of the experimentally preferred NO orientations. In a few cases, the calculations reproduce the experimentally observed orientations only when the whole protein is taken into consideration.

Nitric oxide activation facilitated by cooperative multimetallic electron transfer within an iron-functionalized polyoxovanadate-alkoxide cluster

Cooperative multimetallic electron transfer to accommodate substrate binding.

A series of NO-bound, iron-functionalized polyoxovanadate–alkoxide (FePOV–alkoxide) clusters have been synthesized, providing insight into the role of multimetallic constructs in the coordination and activation of a substrate. Upon exposure of the heterometallic cluster to NO, the vanadium-oxide metalloligand is oxidized by a single electron, shuttling the reducing equivalent to the {FeNO} subunit to form a {FeNO}⁷ species. Four NO-bound clusters with electronic distributions ranging from [VV3VIV2]{FeNO}⁷ to [VIV5]{FeNO}⁷ have been synthesized, and characterized via¹H NMR, infrared, and electronic absorption spectroscopies. The ability of the FePOV–alkoxide cluster to store reducing equivalents in the metalloligand for substrate coordination and activation highlights the ultility of the metal-oxide scaffold as a redox reservoir.

Influence of postmortem treatment with nitric oxide on the muscle color and color stability of tilapia (Oreochromis niloticus) fillets

BACKGROUND

Nitric oxide (NO) has been recognized as pivotal for color and color stability of meat products and has an evident effect on inhibiting microbial growth in processed meat. The use of indirect NO (nitrate/nitrite) in industrial meat curing has potential deleterious effects and great concerns have been expressed over residual nitrite in meat after curing. To find a succedaneum, we have demonstrated the influence of direct NO (saturated NO solution) through euthanasia before slaughter on the fillets color of tilapia and the results suggested that direct NO treatment prior to slaughter is a good procedure to improve the color of tilapia fillets.

OBJECTIVE

To further investigate the effect of direct NO on the muscle color and shelf-life of fillets from tilapia, this study was conducted to investigate the muscle color and color stability of tilapia fillets postmortem treated with saturated NO solution and their shelf-life during refrigerated storage.

METHODS

Tilapia fillets were immersed in a saturated NO solution for 13 min, vacuum-packed and stored at refrigerated temperature for 15 days. Visual observations, color values and absorption maxima were used to evaluate the muscle color and color stability of tilapia fillets. Total volatile basic nitrogen (TVB-N) values were used to evaluate the shelf-life of tilapia fillets during refrigerated storage.

RESULTS

By visual observation, NO treated tilapia fillets showed a brighter red color as compered to control samples after NO-treatment and during the whole storage. The redness (a*) values of NO treated tilapia fillets were significantly increased (P < 0.05) after NO-treatment, continuously increased (P < 0.05) during the earlier 9 days of the storage and remained roughly unchanged during the rest days of the storage. While the a* values of control samples decreased progressively during the storage. NO-treatment effectively improved the muscle color and color stability of tilapia fillets. The peak wavelengths of extract from the muscles of NO treated tilapia fillets increased from 418 nm to 421 nm at 15 d of the storage, while that of control decreased from 418 nm to 410 nm, indicated that color improvement in NO-treated tilapia fillets is mainly due to the formation of MbNO. Moreover, NO-treatment resulted in less TVB-N values than control (16.06 and 21.93 mg of N/100 g at the end of the storage, respectively), prolonging the shelf-life of tilapia fillets.

CONCLUSION

The results suggested that postmortem treatment with NO is a good procedure not only for improving the muscle color and color stability but also for prolonging the shelf-life of tilapia fillets during the storage, which is valuable for industrial manufacturing of tilapia and possibly for other fish species.

Antibacterial nitric oxide- and singlet oxygen-releasing polystyrene nanoparticles responsive to light and temperature triggers

Novel therapies to prevent bacterial infections are of utmost importance in biomedical research due to the emergence of multidrug-resistant strains of bacteria. Herein, we report the preparation, characterization and antibacterial evaluation of sulfonated polystyrene nanoparticles simultaneously releasing two antibacterial species, nitric oxide (NO) and singlet oxygen (O₂(¹Δ_g)), upon irradiation with visible light. The nanoparticles were prepared by simple and scalable processes from nanofiber membranes with an encapsulated NO photodonor and/or ionically entangled tetracationic porphyrin/phthalocyanine photosensitizers. The release of NO and O₂(¹Δ_g) from the polystyrene nanoparticles is controlled by light wavelength and dose, as well as by temperature, which influences the diffusion coefficient and solubility of both species in the polystyrene matrix. The concentrations of NO and O₂(¹Δ_g) were measured by amperometric and time-resolved spectroscopic techniques and by chemical analysis. Due to the efficient photogeneration of both species at physiological temperature and resultant strong antibacterial action observed on Escherichia coli, the nanoparticles are a promising material for antibacterial applications triggered/modulated by light and temperature.

Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re-evaluating the safety of sodium nitrate (E 251) and potassium nitrate (E 252) when used as food additives. The current acceptable daily intakes (ADIs) for nitrate of 3.7 mg/kg body weight (bw) per day were established by the SCF (1997) and JECFA (2002). The available data did not indicate genotoxic potential for sodium and potassium nitrate. The carcinogenicity studies in mice and rats were negative. The Panel considered the derivation of an ADI for nitrate based on the formation of methaemoglobin, following the conversion of nitrate, excreted in the saliva, to nitrite. However, there were large variations in the data on the nitrate-to-nitrite conversion in the saliva in humans. Therefore, the Panel considered that it was not possible to derive a single value of the ADI from the available data. The Panel noticed that even using the highest nitrate-to-nitrite conversion factor the methaemoglobin levels produced due to nitrite obtained from this conversion would not be clinically significant and would result to a theoretically estimated endogenous N-nitroso compounds (ENOC) production at levels which would be of low concern. Hence, and despite the uncertainty associated with the ADI established by the SCF, the Panel concluded that currently there was insufficient evidence to withdraw this ADI. The exposure to nitrate solely from its use as a food additive was estimated to be less than 5% of the overall exposure to nitrate in food based on a refined estimated exposure scenario. This exposure did not exceed the current ADI (SCF, 1997). However, if all sources of exposure to dietary nitrate are considered (food additive, natural presence and contamination), the ADI would be exceeded for all age groups at the mean and the highest exposure.