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Title: Structural and Mechanistic Insights into Hemoglobin-catalyzed Hydrogen Sulfide Oxidation and the Fate of Polysulfide Products

Abstract

Hydrogen sulfide is a cardioprotective signaling molecule but is toxic at elevated concentrations. Red blood cells can synthesize H2S but, lacking organelles, cannot dispose of H2S via the mitochondrial sulfide oxidation pathway. We have recently shown that at high sulfide concentrations, ferric hemoglobin oxidizes H2S to a mixture of thiosulfate and iron-bound polysulfides in which the latter species predominates. Here, we report the crystal structure of human hemoglobin containing low spin ferric sulfide, the first intermediate in heme-catalyzed sulfide oxidation. The structure provides molecular insights into why sulfide is susceptible to oxidation in human hemoglobin but is stabilized against it in HbI, a specialized sulfide-carrying hemoglobin from a mollusk adapted to life in a sulfide-rich environment. We have also captured a second sulfide bound at a postulated ligand entry/exit site in the α-subunit of hemoglobin, which, to the best of our knowledge, represents the first direct evidence for this site being used to access the heme iron. Hydrodisulfide, a postulated intermediate at the junction between thiosulfate and polysulfide formation, coordinates ferric hemoglobin and, in the presence of air, generated thiosulfate. At low sulfide/heme iron ratios, the product distribution between thiosulfate and iron-bound polysulfides was approximately equal. The iron-bound polysulfides weremore » unstable at physiological glutathione concentrations and were reduced with concomitant formation of glutathione persulfide, glutathione disulfide, and H2S. Hence, although polysulfides are unlikely to be stable in the reducing intracellular milieu, glutathione persulfide could serve as a persulfide donor for protein persulfidation, a posttranslational modification by which H2S is postulated to signal.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
National Institutes of Health (NIH)
OSTI Identifier:
1351356
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Biological Chemistry; Journal Volume: 292; Journal Issue: 13
Country of Publication:
United States
Language:
ENGLISH
Subject:
59 BASIC BIOLOGICAL SCIENCES; 60 APPLIED LIFE SCIENCES

Citation Formats

Vitvitsky, Victor, Yadav, Pramod K., An, Sojin, Seravalli, Javier, Cho, Uhn-Soo, and Banerjee, Ruma. Structural and Mechanistic Insights into Hemoglobin-catalyzed Hydrogen Sulfide Oxidation and the Fate of Polysulfide Products. United States: N. p., 2017. Web. doi:10.1074/jbc.M117.774943.
Vitvitsky, Victor, Yadav, Pramod K., An, Sojin, Seravalli, Javier, Cho, Uhn-Soo, & Banerjee, Ruma. Structural and Mechanistic Insights into Hemoglobin-catalyzed Hydrogen Sulfide Oxidation and the Fate of Polysulfide Products. United States. doi:10.1074/jbc.M117.774943.
Vitvitsky, Victor, Yadav, Pramod K., An, Sojin, Seravalli, Javier, Cho, Uhn-Soo, and Banerjee, Ruma. Fri . "Structural and Mechanistic Insights into Hemoglobin-catalyzed Hydrogen Sulfide Oxidation and the Fate of Polysulfide Products". United States. doi:10.1074/jbc.M117.774943.
@article{osti_1351356,
title = {Structural and Mechanistic Insights into Hemoglobin-catalyzed Hydrogen Sulfide Oxidation and the Fate of Polysulfide Products},
author = {Vitvitsky, Victor and Yadav, Pramod K. and An, Sojin and Seravalli, Javier and Cho, Uhn-Soo and Banerjee, Ruma},
abstractNote = {Hydrogen sulfide is a cardioprotective signaling molecule but is toxic at elevated concentrations. Red blood cells can synthesize H2S but, lacking organelles, cannot dispose of H2S via the mitochondrial sulfide oxidation pathway. We have recently shown that at high sulfide concentrations, ferric hemoglobin oxidizes H2S to a mixture of thiosulfate and iron-bound polysulfides in which the latter species predominates. Here, we report the crystal structure of human hemoglobin containing low spin ferric sulfide, the first intermediate in heme-catalyzed sulfide oxidation. The structure provides molecular insights into why sulfide is susceptible to oxidation in human hemoglobin but is stabilized against it in HbI, a specialized sulfide-carrying hemoglobin from a mollusk adapted to life in a sulfide-rich environment. We have also captured a second sulfide bound at a postulated ligand entry/exit site in the α-subunit of hemoglobin, which, to the best of our knowledge, represents the first direct evidence for this site being used to access the heme iron. Hydrodisulfide, a postulated intermediate at the junction between thiosulfate and polysulfide formation, coordinates ferric hemoglobin and, in the presence of air, generated thiosulfate. At low sulfide/heme iron ratios, the product distribution between thiosulfate and iron-bound polysulfides was approximately equal. The iron-bound polysulfides were unstable at physiological glutathione concentrations and were reduced with concomitant formation of glutathione persulfide, glutathione disulfide, and H2S. Hence, although polysulfides are unlikely to be stable in the reducing intracellular milieu, glutathione persulfide could serve as a persulfide donor for protein persulfidation, a posttranslational modification by which H2S is postulated to signal.},
doi = {10.1074/jbc.M117.774943},
journal = {Journal of Biological Chemistry},
number = 13,
volume = 292,
place = {United States},
year = {Fri Feb 17 00:00:00 EST 2017},
month = {Fri Feb 17 00:00:00 EST 2017}
}
  • Electron spin resonance (ESR) experiments on the oxidation of hydrogen sulfide were performed in the temperature range 20-150/sup 0/C. Alumina, active carbon, and molecular sieve zeolite 13X were investigated as catalysts. For zeolite 13X it was demonstrated that the reaction is autocatalytic and that sulfur radicals are the active sites for oxygen chemisorption. The intensity of the sulfur radical ESR signal, which is related to the degree of conversion of these radicals, by oxygen, fits in with an oxidation-reduction mechanism. The sulfur-oxygen radical species, which appear when oxygen is admitted to sulfur radicals, are assigned to sulfur chains containing onemore » or two oxygen atoms at the end of the chain. It is very likely that these sulfur-oxygen radicals are intermediates in the proposed mechanism. The formation of the by-product SO/sub 2/ from S/sub x/O/sub 2/.-at temperatures above 175/sup 0/C is also visible in the ESR spectrum. On the basis of the experiments it is concluded that in the mechanism of H/sub 2/S oxidation on active carbons, carbon radicals do not play an important role.« less
  • The kinetics of the catalytic oxidation of hydrogen sulfide by molecular oxygen have been studied in the temperature range 20-250/sup 0/C. The primary reaction product is sulfur which may undergo further oxidation to SO/sub 2/ at temperatures above 200/sup 0/C. From the kinetics of this autocatalytic reaction an oxidation-reduction mechanism was derived. The two rate influencing steps are the chemisorption of oxygen and the reaction between dissociatively chemisorbed H/sub 2/S and chemisorbed oxygen. The high activation energy for the formation of SO/sub 2/ (120 kJ mol/sup -1/) explains the high selectivity towards sulfur, although SO/sub 2/ is thermodynamically the mostmore » favored product. At temperatures above 300/sup 0/C, where the formation of SO/sub 2/ occurs readily, the SO/sub 2/ may be an intermediate in the reaction of H/sub 2/S with O/sub 2/ leading to S and H/sub 2/O.« less
  • Catalytic pathways for acetic acid (CH3COOH) and hydrogen (H2) reactions on dispersed Ru clusters in the aqueous medium and the associated kinetic requirements for C-O and C-C bond cleavages and hydrogen insertion are established from rate and isotopic assessments. CH3COOH reacts with H2 in steps that either retain its carbon backbone and lead to ethanol, ethyl acetate, and ethane (47-95 %, 1-23 %, and 2-17 % carbon selectivities, respectively) or break its C-C bond and form methane (1-43 % carbon selectivities) at moderate temperatures (413-523 K) and H2 pressures (10-60 bar, 298 K). Initial CH3COOH activation is the kinetically relevantmore » step, during which CH3C(O)-OH bond cleaves on a metal site pair at Ru cluster surfaces nearly saturated with adsorbed hydroxyl (OH*) and acetate (CH3COO*) intermediates, forming an adsorbed acetyl (CH3CO*) and hydroxyl (OH*) species. Acetic acid turnover rates increase proportionally with both H2 (10-60 bar) and CH3COOH concentrations at low CH3COOH concentrations (<0.83 M), but decrease from first to zero order as the CH3COOH concentration and the CH3COO* coverages increase and the vacant Ru sites concomitantly decrease. Beyond the initial CH3C(O)-OH bond activation, sequential H-insertions on the surface acetyl species (CH3CO*) lead to C2 products and their derivative (ethanol, ethane, and ethyl acetate) and the competitive C-C bond cleavage of CH3CO* causes the eventual methane formation. The instantaneous carbon selectivities towards C2 species (ethanol, ethane, and ethyl acetate) increase linearly with the concentration of proton-type Hδ+ (derived from carboxylic acid dissociation) and chemisorbed H*. The selectivities towards C2 products decrease with increasing temperature, because of higher observed barriers for C-C bond cleavage than H-insertion. This study offers an interpretation of mechanism and energetics and provides kinetic evidence of carboxylic acid assisted proton-type hydrogen (Hδ+) shuffling during H-insertion steps in the aqueous phase, unlike those in the vapor phase, during the hydrogenation of acetic acid on Ru clusters.« less
  • The catalytic oxidation of simple cyclic ketones with hydrogen peroxide to give the corresponding lactones is reported. The reaction is catalyzed by complexes of Pt(II) of the type [(P-P)Pt(CF[sub 3])(solv)][sup +] (P-P = diphosphine) that may be deactivated by the hydroxy acids formed by hydrolysis of the lactones. The selectivity of the catalyst is studied in the oxidation of substrates like camphor, 2-cyclohexene-1-one, menthone, carvone, and indanones. Cyclobutanone is used to determine the mechanism of the reaction from initial rates studies. The reaction scheme proposed, which accounts for the observed effects of the various reactants, involves the coordination of themore » ketone on the vacant coordination site of the complex followed by nucleophilic attack of free hydrogen peroxide on the carbonyl carbon. The involvement of a quasi-peroxymetallacyclic intermediate is suggested which rearranges to give the lactone and the starting complex. A comparison with the mechanistic behavior of organic peroxy acids is given. 24 refs., 10 figs., 3 tabs.« less