Impact of the dynamics of the catalytic arginine on nitrite and chlorite binding by dimeric chlorite dismutase

Compound I Formation and Reactivity in Dimeric Chlorite Dismutase: Impact of pH and the Dynamics of the Catalytic Arginine

“…All purified proteins showed a dimeric state, high purity (>90%), and an average Reinheitszahl ( A Soret / A 280 ) of 2.2, which demonstrates almost 100% heme occupancy (data not shown). UV–vis spectroscopic measurements at acidic and neutral pH demonstrate that the three heme proteins are in the ferric high-spin state, characterized by a Soret maximum at 406/408 nm; Q-bands at 502, 535, and 575 nm; and a charge transfer (CT)-band at 635 nm. − Addition of a 1000-fold excess of serotonin, which in the following experiments is used as a one-electron donor of C Cld redox intermediates, had no impact on the electronic configuration of these iron-proteins as demonstrated by both UV–vis and ECD in the respective heme absorption area as well as by EPR spectroscopies (Figure S1 and Figure A,B). As serotonin exhibits strong absorbance maxima at 276 and 298 nm, this area is not shown in the UV–vis spectra.…”

“…The crucial question is the following: Why is chlorite consumption in Clds always coupled to O 2 generation, and why is chlorite consumption in all other heme systems, including peroxidases, always strictly uncoupled from O 2 generation? Importantly, in all Cld arginine mutants studied so far, Cl–O bond cleavage is always coupled with O 2 generation, even in those having the catalytic arginine exchanged by alanine, despite the fact that these variants exhibit very low activities and are prone to inactivation. ,, This might suggest that the hydrophobic and sterically confined nature of the Cld distal pocket is important for protecting the reactive intermediates and prompting their conversion by a rebound mechanism.…”

Roles of High-Valent Hemes and pH Dependence in Halite Decomposition Catalyzed by Chlorite Dismutase fromDechloromonas aromatica

“…The most widely accepted hypothesis is that the halite coordinates through one of its terminal oxo groups to the coordinately unsaturated heme of the resting enzyme. Although there is no direct structural evidence of this ES coordination mode, the structure of its second-row nitrogen-based substrate analogue, NO 2 – , is known from the crystal structures of nitrite complexes of Da Cld and CCld. , These structures revealed nitrite to be coordinated in its nitrito mode, i.e., through one of the terminal oxo groups. Evidence from the kinetics and thermodynamics of anionic ligand binding supports a crucial role for the positively charged guanidinium group of distal Arg183.…”

“…Evidence from the kinetics and thermodynamics of anionic ligand binding supports a crucial role for the positively charged guanidinium group of distal Arg183. It is clear that this positive charge, which can interact strongly with the ligand before and during its coordination to the heme by virtue of its close proximity to the heme iron center, drives and stabilizes the enzyme:subtrate complex. ,,,,, …”

“…It is clear that this positive charge, which can interact strongly with the ligand before and during its coordination to the heme by virtue of its close proximity to the heme iron center, drives and stabilizes the enzyme:subtrate complex. 3,29,31,32,57,58 2. DaCld−OXO − Formation is Followed by Rapid Heterolytic O−XO − Bond Scission.…”