Photothermal studies of CO photodissociation from mixed valence Escherichia coli cytochrome bo3

Abstract

Here, we report the volume and enthalpy changes accompanying CO photodissociation from the mixed valence form of cytochrome bo 3 oxidase from Escherichia coli. The results of photoacoustic calorimetry indicate two kinetic phases with distinct volume and enthalpy changes accompanying CO photodissociation from heme o 3 and its transfer to Cu B. The first phase occurring on a timescale of <50 ns is characterized by a volume decrease of −1.3 ± 0.3 mL mol −1 and enthalpy change of 32 ± 1.6 kcal mol −1. Subsequently, a volume increase of 2.9 mL mol −1 with an enthalpy change of −5.3 ± 2.5 kcal mol −1 is observed with the lifetime of ∼250 ns (this phase has not been detected in previous optical studies). These volume and enthalpy changes differ from the volume and enthalpy changes observed for CO dissociation from fully reduced cytochrome bo 3 oxidase indicating that the heme o 3/Cu B active site dynamics are affected by the redox state of heme b.