%0 Conference Proceedings %T Heme a3-NO interactions in reduced cytochrome c oxidases: binding and recombination dynamics %+ Laboratoire d'optique et biosciences (LOB) %+ Institut de biologie physico-chimique (IBPC (FR_550)) %A Vos, Marten, H. %A Pilet, Eric %A Nitschke, W. %A Rappaport, F. %A Soulimane, T. %A Lambry, Jean-Christophe %A Liebl, Ursula %< avec comité de lecture %( BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS %B 13th EUROPEAN BIOENERGETICS CONFERENCE %C Pisa, Italy %V 1658 %N 1-2, EBEC Short Reports Volume 13 %P 159 %8 2004-08-21 %D 2004Conference papers %X Cytochrome c oxidase (CcO) has a high affinity for nitric oxide (NO), a property in the regulation of respiration [1]. We have previously shown that recombination kinetics of reduced CcO -NO from P. denitrificans on the picosecond time scale depend strongly on the NO:enzyme stoichiometry and inferred that more than one NO can be accomodated by the active site [2], already at mildly suprastoichimetric NO concentrations. We have now largely extended these studies by studying rebinding dynamics from the picosecond up to the microsecond time scale, by performing parallel steady-state EPR characterizations under similar conditions as the optical experiments, and comparing them with molecular modeling results. A comparative study was performed on CcO ba3 from T. thermophilus, where two NO molecules cannot be copresent in the active site in steady state due to its NO reductase activity [3]. The kinetic results allow to discriminate between different models of NOdependent recombination and show that the overall NO-escape probability out of the protein is high when only one NO is bound to aa3, whereas strong rebinding on the 15-ns time scale was observed for ba3. The EPR characterizations show similar results for aa3 at substoichiometries NO:enzyme ratios and for ba3, indicating formation of a six-coordinate heme-NO complex. The presence of a second NO molecule in the aa3 active site strongly modifies the heme-NO EPR spectrum, and can be rationilized by a rotation of the NO with respect to the proximal histidine. This proposal is consistent with molecular modeling studies. The binding properties of the second NO molecule will also be discussed. %G English %L hal-00845029 %U https://polytechnique.hal.science/hal-00845029 %~ X %~ CNRS %~ X-LOB %~ X-DEP %~ X-DEP-BIO %~ SORBONNE-UNIVERSITE %~ SU-INF-2018 %~ ALLIANCE-SU