NO binding and ultrafast dynamics in the active site of reduced heme-copper oxidases

Eric Pilet (1) , Gérard Lipowski (1) , T. Soulimane (2) , Ursula Liebl (1) , Marten H. Vos (1)

1 LOB - Laboratoire d'optique et biosciences
2 Paul Scherrer Institute

Nitric oxide (NO) is involved in regulation of respiration through interaction with the active site of cytochrome c oxidase (CcO) [1]. We study the dynamics of NO in this site in its fully reduced form by femtosecond flash photolysis. These are complicated, as more than one NO can be accommodated in or near the active site, even at very low NO concentrations [2]. By extending our measurements to the nanosecond timescale, here we show that two distinct phase of recombination of NO with heme a3 can be observed: a slow phase ( > 4 ns) which is the only phase observed at low (up to stoichiometric) NO concentrations (1 NO/enzyme), and a faster one (f250 ps) with an increasingly higher relative amplitude at higher concentrations (2 NO/enzyme). Interestingly, in CcO ba3 from Thermus thermophilus the kinetics are NO-concentration independent and consist of the slow phase only. This protein is known to have a considerable NO reductase activity [3], which prevents the steady-state simultaneous presence of 2 NO molecules in the reduced active site. Additional techniques are presently explored to test various models of NO binding and dynamics in the binuclear center

Eric Pilet, Gérard Lipowski, T. Soulimane, Ursula Liebl, Marten H. Vos. NO binding and ultrafast dynamics in the active site of reduced heme-copper oxidases. EBEC 2022 : 12th European Bioenergetics Conference, Sep 2002, Arcachon, France. pp.99. ⟨hal-00845091⟩