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10.1021/jacs.7b07507 http://scihub22266oqcxt.onion/10.1021/jacs.7b07507 C5976446!5976446!28984134     free     free     free Deprecated: Implicit conversion from float 211.6 to int loses precision in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 534 Deprecated: Implicit conversion from float 211.6 to int loses precision in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 534 Deprecated: Implicit conversion from float 211.6 to int loses precision in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 534 Deprecated: Implicit conversion from float 211.6 to int loses precision in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 534 Deprecated: Implicit conversion from float 211.6 to int loses precision in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 534       J+Am+Chem+Soc 2017 ; 139 (44): 15738-47 Nephropedia Template TP {{tp|p=28984134|t=2017. Ultrafast CO kinetics in heme proteins: adiabatic ligand binding and heavy atom tunneling |pdf=|usr=}}{{28984134}} gab.com Text Ultrafast CO kinetics in heme proteins: adiabatic ligand binding and heavy atom tunneling JO: J Am Chem Soc http://www.kidney.de/pget.php?&tw=1&pmid=28984134 #FOAvip We report on the ultrafast kinetics of CO rebinding to carbon monoxide oxidation activator protein (ChCooA) over a wide temperature range and make comparisons with the kinetics of CO and NO binding to protoheme (Fe protoporphyrin IX) and myoglobin (Mb). The CO binding to ChCooA is non-exponential over many decades in time at all temperatures studied, including room temperature. To describe this kinetic response we use a linear coupling model with a distribution of enthalpic rebinding barriers that is attributed primarily to protein-induced heterogeneity in the heme doming conformation (distributed barrier model, DBM). Above the solvent glass transition (Tg ~180K), CO rebinding kinetics displays an anti-Arrhenius behavior (i.e., the rate decreases as temperature increases) and this is ascribed to an evolution of the distribution toward increased heme doming and larger enthalpic barriers. Between Tg and ~60K, the non-exponential rebinding slows down as the temperature is lowered and the survival fraction follows the predictions expected for a quenched barrier distribution. However, below ~60K the rebinding kinetics do not continue to slow as predicted by the thermally activated DBM. A possible explanation for this behavior is explored that involves quantum mechanical tunneling of the iron atom along the heme doming coordinate. When the ultrafast CO rebinding kinetics of CooA are compared to the much slower CO rebinding in myoglobin, a two order-of-magnitude increase in the Arrhenius prefactor, from ~109 s?1 to ~1011 s?1, is revealed. A similar prefactor is found for NO binding to CooA, which is typical for NO rebinding to ferrous heme systems. Because kinetic studies of CO rebinding to protoheme also reveal prefactors near ~1011 s?1, we revisit the commonly held view that the CO binding reaction is non-adiabatic due to spin-forbidden (?S=2) selection rules. A non-adiabatic sequential mechanism, involving first order (?S=1) transitions, is considered as a possible explanation for ultrafast CO rebinding; however, the relative crossing energies of the relevant spin states leads us to conclude that the CO ligand binding reaction is adiabatic rather than non-adiabatic and that entropic factors, rather than spin-selection rules, are the cause of the reduced Arrhenius prefactor for CO binding in Mb and Hb. Twit Text FOAVip Ultrafast CO kinetics in heme proteins: adiabatic ligand binding and heavy atom tunneling ????J Am Chem Soc http://www.kidney.de/pget.php?&tw=1&pmid=28984134 #FOAvip Twit Text # Free Paper on # # # # # LINK http://www.kidney.de/pget.php?&tw=1&pmid=28984134 #FOAvip English Wikipedia <ref>{{Cite pmid|28984134}}</ref> Ultrafast CO kinetics in heme proteins: adiabatic ligand binding and heavy atom tunneling #MMPMID28984134 Benabbas A; Sun Y; Poulos TL; Champion PM J Am Chem Soc 2017[Nov]; 139 (44): 15738-47 PMID28984134show ga We report on the ultrafast kinetics of CO rebinding to carbon monoxide oxidation activator protein (ChCooA) over a wide temperature range and make comparisons with the kinetics of CO and NO binding to protoheme (Fe protoporphyrin IX) and myoglobin (Mb). The CO binding to ChCooA is non-exponential over many decades in time at all temperatures studied, including room temperature. To describe this kinetic response we use a linear coupling model with a distribution of enthalpic rebinding barriers that is attributed primarily to protein-induced heterogeneity in the heme doming conformation (distributed barrier model, DBM). Above the solvent glass transition (Tg ~180K), CO rebinding kinetics displays an anti-Arrhenius behavior (i.e., the rate decreases as temperature increases) and this is ascribed to an evolution of the distribution toward increased heme doming and larger enthalpic barriers. Between Tg and ~60K, the non-exponential rebinding slows down as the temperature is lowered and the survival fraction follows the predictions expected for a quenched barrier distribution. However, below ~60K the rebinding kinetics do not continue to slow as predicted by the thermally activated DBM. A possible explanation for this behavior is explored that involves quantum mechanical tunneling of the iron atom along the heme doming coordinate. When the ultrafast CO rebinding kinetics of CooA are compared to the much slower CO rebinding in myoglobin, a two order-of-magnitude increase in the Arrhenius prefactor, from ~109 s?1 to ~1011 s?1, is revealed. A similar prefactor is found for NO binding to CooA, which is typical for NO rebinding to ferrous heme systems. Because kinetic studies of CO rebinding to protoheme also reveal prefactors near ~1011 s?1, we revisit the commonly held view that the CO binding reaction is non-adiabatic due to spin-forbidden (?S=2) selection rules. A non-adiabatic sequential mechanism, involving first order (?S=1) transitions, is considered as a possible explanation for ultrafast CO rebinding; however, the relative crossing energies of the relevant spin states leads us to conclude that the CO ligand binding reaction is adiabatic rather than non-adiabatic and that entropic factors, rather than spin-selection rules, are the cause of the reduced Arrhenius prefactor for CO binding in Mb and Hb. äUltrafast CO kinetics in heme proteins: adiabatic ligand binding and h(epmc).pdf DeepDyve Pubget Overpricing