Spectroscopic evidence supporting neutral thiol ligation to ferrous heme iron

Soluble guanylate cyclase is an NO-sensing hemoprotein that serves as a NO receptor in NO-mediated signaling pathways. It has been believed that this enzyme displays no measurable affinity for O2, thereby enabling the selective NO sensing in aerobic environments. Despite the physiological significance, the reactivity of the enzyme-heme for O2 has not been examined in detail. In this paper we demonstrated that the high spin heme of the ferrous enzyme converted to a low spin oxyheme (Fe2+-O2) when frozen at 77 K in the presence of O2. The ligation of O2 was confirmed by EPR analyses using cobalt-substituted enzyme. The oxy form was produced also under solution conditions at −7 °C, with the extremely low affinity for O2. The low O2 affinity was not caused by a distal steric protein effect and by rupture of the Fe2+-proximal His bond as revealed by extended x-ray absorption fine structure. The midpoint potential of the enzyme-heme was +187 mV, which is the most positive among high spin protoheme-hemoproteins. This observation implies that the electron density of the ferrous heme iron is relatively low by comparison to those of other hemoproteins, presumably due to the weak Fe2+-proximal His bond. Based on our results, we propose that the weak Fe2+-proximal His bond is a key determinant for the low O2 affinity of the heme moiety of soluble guanylate cyclase.

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ChemInform Abstract: Phosphine Binding as a Structural Probe of the Chloroperoxidase Active Sitc: Spectroscopic Evidence for Endogenous Thiolate Ligation to the Heme Iron

Chemischer Informationsdienst ◽

10.1002/chin.198614061 ◽

1986 ◽

Vol 17 (14) ◽

Author(s):

M. SONO ◽

J. H. DAWSON ◽

L. P. HAGER

Keyword(s):

Heme Iron ◽

Spectroscopic Evidence ◽

Structural Probe

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Dietary Heme Iron does not Prevent Postgastrectomy Anemia but Fructooligosaccharides Improve Bioavailability of Heme Iron in Rats

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831.69.5.348 ◽

1999 ◽

Vol 069 (05) ◽

pp. 0348-0355 ◽

Cited By ~ 20

Author(s):

A. Ohta ◽

K. Sakai ◽

M. Takasaki ◽

M. Uehara ◽

T. Tokunaga ◽

...

Keyword(s):

Heme Iron

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Meat and Meat Products Consumption in Italy: Contribution to Trace Elements, Heme Iron and selected B Vitamins supply

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831.74.4.247 ◽

2004 ◽

Vol 74 (4) ◽

pp. 247-251 ◽

Cited By ~ 13

Author(s):

Lombardi-Boccia ◽

Lanzi ◽

Lucarini ◽

Di Lullo

Keyword(s):

Trace Elements ◽

Daily Intake ◽

Meat Products ◽

Heme Iron ◽

B Vitamins ◽

Zinc Intake ◽

Consumption Frequency ◽

Iron And Zinc ◽

Iron Heme ◽

Daily Intakes

This study was undertaken to estimate the contribution of meat and meat products consumption to the daily intakes of trace elements (Fe, Zn, Cu, Se), heme iron, and selected B vitamins (thiamine, riboflavin, niacin) in Italy. Meat and meat products were selected on the basis of their consumption frequency reported by the most recent nationwide dietary individual survey carried out in Italy (INN-CA study). The daily intakes of total iron and heme iron were 1.65 and 1.13 mg/person/day. Zinc intake was 3.65 mg/person/day. Beef made the main contribution to iron, heme iron, and zinc daily intakes. Copper daily intake was 107.3 mug/person/day, with meat products provided the highest contribution (40 mug/person/day). Daily intake of selenium (7.14 mug/person/day) was provided mainly by poultry consumption. Thiamine intake was 228 mug/person/day, and meat products were the main source (110 mug/person/day). Riboflavin intake was 136 mug/person/day, with both beef and meat products as the main contributors (40 mug/person/day). Niacin intake was 7.53 mg/person/day, and poultry was the main source (2.28 mg/person/day). Meat and meat products were a valuable source of micronutrients, supplying 47, 48, and 24% of zinc, niacin, and thiamin daily requirements, respectively, and over 10% of iron, copper, selenium, and riboflavin daily average requirement values of the italian RDAs calculated for the population involved in the survey (INN-CA study).

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NADH in Solution: A Single State

10.26434/chemrxiv.8208407.v1 ◽

2019 ◽

Author(s):

Joachim Hönes ◽

Julia Wack ◽

Katja Schmitz

Keyword(s):

Aqueous Solution ◽

Base Stacking ◽

Spectroscopic Evidence ◽

Single State

<div>Spectroscopic evidence is presented to show that NADH in aqueous solution does not exist as a folded/unfolded equilibrium but as a single state. The molecule is folded but without base stacking between dihydronicotinamide and adenine.<br></div>

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Strongly Coupled Redox-Linked Conformational Switching at the Active Site of the Non-Heme Iron-Dependent Dioxygenase, TauD

10.26434/chemrxiv.9461462 ◽

2019 ◽

Author(s):

Christopher John ◽

Greg M. Swain ◽

Robert P. Hausinger ◽

Denis A. Proshlyakov

Keyword(s):

Active Site ◽

Structural Model ◽

Heme Iron ◽

Chemical Transformations ◽

Experimental Conditions ◽

Strongly Coupled ◽

Non Heme Iron ◽

Reversible Redox ◽

Wide Range ◽

Complex Structural

2-Oxoglutarate (2OG)-dependent dioxygenases catalyze C-H activation while performing a wide range of chemical transformations. In contrast to their heme analogues, non-heme iron centers afford greater structural flexibility with important implications for their diverse catalytic mechanisms. We characterize an <i>in situ</i> structural model of the putative transient ferric intermediate of 2OG:taurine dioxygenase (TauD) by using a combination of spectroelectrochemical and semi-empirical computational methods, demonstrating that the Fe (III/II) transition involves a substantial, fully reversible, redox-linked conformational change at the active site. This rearrangement alters the apparent redox potential of the active site between -127 mV for reduction of the ferric state and 171 mV for oxidation of the ferrous state of the 2OG-Fe-TauD complex. Structural perturbations exhibit limited sensitivity to mediator concentrations and potential pulse duration. Similar changes were observed in the Fe-TauD and taurine-2OG-Fe-TauD complexes, thus attributing the reorganization to the protein moiety rather than the cosubstrates. Redox difference infrared spectra indicate a reorganization of the protein backbone in addition to the involvement of carboxylate and histidine ligands. Quantitative modeling of the transient redox response using two alternative reaction schemes across a variety of experimental conditions strongly supports the proposal for intrinsic protein reorganization as the origin of the experimental observations.

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