Protein nitration induced by Hemin/NO: A complementary mechanism through the catalytic functions of hemin and NO-scavenging

Hemin and heme-peroxidases have been considered essential catalysts for the nitrite/hydrogen peroxide (H₂O₂)-mediated protein nitration in vitro, understood as one of the main pathways for protein modification in biological systems. However, the role of nitric oxide (^●NO) in the heme/hemin-induced protein nitration has not been studied in-depth. This is despite its reductive nitrosylating effects following binding to hemin and the possible involvement of the reactive nitrogen species in the nitration of various functional proteins. Here, the ^●NO-binding affinity of hemin has been studied along with the influence of ^●NO on the internalization of hemin into MDA-MB-231 cells and the accompanying changes in the profile of intracellular nitrated proteins. Moreover, to further understand the mechanism involved, bovine serum albumin (BSA) nitration was studied after treatment with hemin and ^●NO, with an investigation of the effects of pH of the reaction medium, generation of H₂O₂, and the oxidation of the tyrosine residues as the primary sites for the nitration. We demonstrated that hemin nitrosylation enhanced its cellular uptake and induced the one-electron oxidation and nitration of different intracellular proteins along with its ^●NO-scavenging efficiency. Moreover, the hemin/NO-mediated BSA nitration was proved to be dependent on the concentration of ^●NO and the pH of the reaction medium, with a vital role being played by the scavenging effects of protein for the free hemin molecules. Collectively, our results reaffirm the involvement of hemin and ^●NO in the nitration mechanism, where the nitrosylation products can induce protein nitration while promoting the effects of the components of the nitrite/H₂O₂-mediated pathway.

Increased antioxidative and nitric oxide scavenging activity of ginseng marc fermented by Pediococcus acidilactici KCCM11614P

This study aimed to improve the antioxidant and nitric oxide scavenging activities of ginseng marc fermented by Pediococcus acidilactici, thereby creating a biofunctional resource with improved anti-inflammatory capability. P. acidilactici was inoculated in 1% ginseng marc extract; cell viability, pH, and total titratable acidity were measured. Total phenolic and flavonoid contents were measured using Folin-Ciocalteu reagent and colorimetric method. Ferric reducing antioxidant power (FRAP), β-carotene, and sodium nitroprusside (SNP) assays were used to evaluate functionality. Polyphenols and flavonoids totaled 33.7 ± 0.4 and 10.0 ± 0.4 mg/g of solid, respectively, at 24 h fermentation. P. acidilactici had 40 nM β-galactosidase and 20 nM β-glucosidase activities. Antioxidative activities increased up to 34.5 and 10.2%, respectively, as measured via FRAP and β-carotene assays. Anti-inflammatory activity of the fermented extract-as measured via SNP assay-increased 342%, suggesting that ginseng marc fermented by P. acidilactici could be used in food or pharmaceutical industries.

Shedding light on NO homeostasis: Light as a key regulator of glutathione and nitric oxide metabolisms during seedling deetiolation

Despite the significant impacts of light on nitric oxide (NO) levels in plants, the mechanism underlying the influence of this environmental factor on NO metabolism remains poorly understood. A critical mechanism controlling NO levels in plant cells relies on the S-nitrosylation of glutathione (GSH), giving rise to S-nitrosoglutathione (GSNO), which can be either stored or degraded depending on the cellular context. Here, we demonstrate that a strict balance is maintained between NO generation and scavenging during tomato (Solanum lycopersicum) seedling deetiolation. Given the absence of accurate methods in the literature to estimate NO scavenging in planta, we first developed a simple, robust system to continuously monitor the global in vivo NO scavenging by plant tissues. Then, using photomorphogenic tomato mutants, we demonstrated that the light-evoked de-etiolation is associated with a dramatic rise in NO content followed by a progressive increment in NO scavenging capacity of the tissues. Light-driven increments in NO scavenging rates coincided with pronounced rises in S-nitrosothiol content and GSNO reductase (GSNOR) activity, thereby suggesting that GSNO formation and subsequent removal via GSNOR might be key for controlling NO levels during seedling deetiolation. Accordingly, treatments with thiol-blocking compounds further indicated that thiol nitrosylation might be critically involved in the NO scavenging mechanism responsible for maintaining NO homeostasis during deetiolation. The impacts of both light and NO on the transcriptional profile of glutathione metabolic genes also revealed an independent but coordinated action of these signals on the regulation of key components of glutathione and GSNO metabolisms. Altogether, these data indicated that GSNO formation and subsequent removal might facilitate maintaining NO homeostasis during light-driven seedling deetiolation.

Scavenging of nitric oxide by hemoglobin in the tunica media of porcine coronary arteries

Scavenging of nitric oxide (NO) often interferes with studies on NO signaling in cell-free preparations. We observed that formation of cGMP by NO-stimulated purified soluble guanylate cyclase (sGC) was virtually abolished in the presence of cytosolic preparations of porcine coronary arteries, with the scavenging activity localized in the tunica media (smooth muscle layer). Electrochemical measurement of NO release from a donor compound and light absorbance spectroscopy showed that cytosolic preparations contained a reduced heme protein that scavenged NO. This protein, which reacted with anti-human hemoglobin antibodies, was efficiently removed from the preparations by haptoglobin affinity chromatography. The cleared cytosols showed only minor scavenging of NO according to electrochemical measurements and did not decrease cGMP formation by NO-stimulated sGC. In contrast, the column flow-through caused a nearly 2-fold increase of maximal sGC activity (from 33.1 ± 1.6 to 54.9 ± 2.2 μmol × min(-1) × mg(-1)). The proteins retained on the affinity column were identified as hemoglobin α and β subunits. The results indicate that hemoglobin, presumably derived from vasa vasorum erythrocytes, is present and scavenges NO in preparations of porcine coronary artery smooth muscle. Selective removal of hemoglobin-mediated scavenging unmasked stimulation of maximal NO-stimulated sGC activity by a soluble factor expressed in vascular tissue.

Haemoglobins of Mycobacteria: structural features and biological functions

The genus Mycobacterium is comprised of Gram-positive bacteria occupying a wide range of natural habitats and includes species that range from severe intracellular pathogens to economically useful and harmless microbes. The recent upsurge in the availability of microbial genome data has shown that genes encoding haemoglobin-like proteins are ubiquitous among Mycobacteria and that multiple haemoglobins (Hbs) of different classes may be present in pathogenic and non-pathogenic species. The occurrence of truncated haemoglobins (trHbs) and flavohaemoglobins (flavoHbs) showing distinct haem active site structures and ligand-binding properties suggests that these Hbs may be playing diverse functions in the cellular metabolism of Mycobacteria. TrHbs and flavoHbs from some of the severe human pathogens such as Mycobacterium tuberculosis and Mycobacterium leprae have been studied recently and their roles in effective detoxification of reactive nitrogen and oxygen species, electron cycling, modulation of redox state of the cell and facilitation of aerobic respiration have been proposed. This multiplicity in the function of Hbs may aid these pathogens to cope with various environmental stresses and survive during their intracellular regime. This chapter provides recent updates on genomic, structural and functional aspects of Mycobacterial Hbs to address their role in Mycobacteria.