Oxidative heme protein-mediated nitroxyl (HNO) generation.

Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109, USA.
Dalton Transactions (Impact Factor: 4.1). 06/2010; 39(22):5203-12. DOI: 10.1039/c000980f
Source: PubMed

ABSTRACT The distinct biological properties of nitroxyl (HNO) have focused research regarding the chemistry and biology of this redox relative of nitric oxide (NO). Much of HNO's biological activity appears to arise through modification of thiol-containing enzymes and proteins and reactions with iron-heme proteins. The reactions of HNO with hemoglobin and myoglobin serve as a general model for understanding HNO reactivity with other heme proteins. Interaction of HNO with catalase and soluble guanylate cyclase may have biological roles. While endogenous HNO formation remains to be described, we summarize work that reveals HNO formation through oxidative heme protein metabolism of various nitrogen-containing substrates including hydroxylamine, hydroxyurea, hydroxamic acids, cyanamide, and sodium azide. Depending on the enzyme, the nascent HNO reductively nitrosylates the heme protein or escapes the heme pocket as HNO. Such results define an alternative metabolism-based route to HNO that may inform endogenous HNO production.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Shedding of organs by abscission is a key terminal step in plant development and stress responses. Cell wall (CW) loosening at the abscission zone can occur through a combination chain breakage of apoplastic polysaccharides and tension release of cellulose microfibrils. Two distinctly regulated abscission cleavage events are amenable to study in small water ferns of the genus Azolla; one is a rapid abscission induced by environmental stimuli such as heat or chemicals, and the other is an ethylene-induced process occurring more slowly through the action of hydrolytic enzymes. Although free radicals are suggested to be involved in the induction of rapid root abscission, its mechanism is not fully understood. The apoplast contains peroxidases, metal-binding proteins and phenolic compounds that potentially generate free radicals from H2O2 to cleave polysaccharides in the CW and middle lamella. Effects of various thiol-reactive agents implicate the action of apoplastic peroxidases having accessible cysteine thiols in rapid abscission. The Ca(2+) dependency of rapid abscission may reflect the stabilization Ca(2+) confers to peroxidase structure and binding to pectin. To spur further investigation, we present a hypothetical model for small signaling molecules H2O2 and NO and their derivatives in regulating, via modification of putative protein thiols, free radical attack of apoplastic polysaccharides.
    Plant Science 03/2014; 217-218:120-6. · 4.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The neutrophil enzyme myeloperoxidase (MPO) promotes oxidative stress in numerous inflammatory pathologies by producing hypohalous acids. Its inadvertent activity is a prime target for pharmacological control. Previously, salicylhydroxamic acid (SHA) was reported to be a weak reversible inhibitor of MPO. We aimed to identify related hydroxamates that are good inhibitors of the enzyme. We report on three hydroxamates as the first potent reversible inhibitors of MPO. The chlorination activity of purified MPO was inhibited by 50% by 5 nM of a trifluoromethyl-substituted aromatic hydroxamate, HX1. The hydroxamates were specific for MPO in neutrophils and more potent toward MPO compared to a broad range of redox enzymes and alternative targets. Surface plasmon resonance measurements showed the strength of binding of hydroxamates to MPO correlated with the degree of enzyme inhibition. The crystal structure of MPO-HX1 revealed the inhibitor was bound within the active site cavity above the heme and blocked the substrate channel. HX1 was a mixed-type inhibitor of the halogenation activity of MPO with respect to both hydrogen peroxide and halide. Spectral analyses demonstrated that hydroxamates can act variably as substrates for MPO and convert the enzyme to a nitrosyl ferrous intermediate. This property was unrelated to their ability to inhibit MPO. We propose that aromatic hydroxamates bind tightly to the active site of MPO and prevent it from producing hypohalous acids. This mode of reversible inhibition has potential for blocking the activity of MPO and limiting oxidative stress during inflammation.
    Journal of Biological Chemistry 11/2013; · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to investigate whether nitroxyl (HNO), a redox variant of the radical gasotransmitter nitric oxide (NO) with therapeutically promising properties, affects colonic ion transport. Changes in short-circuit current (Isc) induced by the HNO donor Angeli's salt were recorded in Ussing chambers. Cytosolic Ca(2+) concentration was measured with fura-2. The nitroxyl donor induced a concentration-dependent increase in Isc across rat distal colon which was due to a stimulation of chloride secretion. The secretion induced by Angeli's salt (5·10(-4)mol/l) was not altered by the NO scavenger 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy-3-oxide (carboxy-PTIO), but was abolished by the HNO scavenger L-cysteine. The response was not dependent on the activity of soluble guanylate cyclase or enteric neurons, but was inhibited by indomethacin. Experiments with apically permeabilized epithelia revealed the activation of basolateral K(+) channels and a stimulation of the current carried by the basolateral Na(+)-K(+)-pump by Angeli's salt. The secretion induced by Angeli's salt was reduced in the absence of extracellular Ca(2+). A prominent increase in the cytosolic Ca(2+) concentration was evoked by Angeli's salt predominantly in subepithelial cells within the submucosa, which had the same dependence on extracellular Ca(2+) as the Angeli's salt-induced Cl(-) secretion. Consequently, Angeli's salt induces a soluble guanylate cyclase-independent, Ca(2+)-dependent Cl(-) secretion via activation of the Na(+)-K(+)-ATPase and of basolateral K(+) channels. Cyclooxygenase metabolites produced within the submucosa seem to be involved in this response.
    European journal of pharmacology 06/2013; · 2.59 Impact Factor

Full-text (2 Sources)

Available from
Jun 4, 2014