Photo-induced dynamics of the heme centers in cytochrome bc₁

Abstract

The ultrafast response of cytochrome bc1 is investigated for the first time, via transient absorption spectroscopy.

Microfluidics for Ultrafast Spectroscopy

“…[6] The resulting decay associated spectra, shown in Figure 11, revealed the clear differences between the b-and c 1 -hemes behaviours within the bc 1 protein complex: while the c 1 -hemes undergo photo-dissociation of their axial ligand as a result of ultrafast laser excitation, the b-hemes were shown to undergo photo-oxidation with a high (> 0.4) quantum yield that is beyond all expectations. The b-heme's high electronic reactivity makes sense in the light of cyt bc 1 having to efficiently fulfil its role in the Q-cycle: it favours the reduction and oxidization of the ubiquinone and ubiquinol, respectively.…”

“…[4] Another example is the monitoring of the heme-ligand dissociation and rebinding dynamics that results from the absorption of a photon such as it is the case of various types of cytochromes. [5,6] The use of non-linear optics, such as in the famous and various kind of optical parametric amplifiers (OPA, Non-collinear OPA and multi-pass OPA) [7] as well as the different pulse shaping devices (in either transmission or reflection), [8] gives the ability to tune both the pump and the probe to the desire wavelength, therefore enabling to excite and to follow a particular molecular transition. For example, in the study of the bacterial reaction centers complexes, being comprise of multiple types of pigments that are spectrally distinct, careful tuning of the pump allows to preferably excite one pigment while living the others in their fundamental state.…”

“…Other chromophores can also serve as electron docking sites and electron carriers. [6] The knowledge gained from such studies is then applied for medical and industrial purposes and used to optimize specific molecular reactions. From these examples, it is possible to understand why the study of biological samples by means of ultrafast transient spectroscopy, among other spectroscopic techniques, became and remains one of the standard analytical tool for the fundamental understanding of a broad range of molecular dynamics.…”

“…In order to illustrate the applicability of the microfluidic flow-cell as well as some of its advantages I present here a unique analysis, that of the Cytochrome (cyt) bc 1 complex. [6] The cyt bc 1 complex is a key player in mitochondrial and bacterial respiratory chains. [21] It is the main actor in the protonmotive Q cycle and results in the formation of a proton gradient across the membrane via a series of embedded hemes as shown in Figure 9.…”

Ultrafast dynamics of the photo-excited hemes b and cnin the cytochrome b6f complex

“…9,10 For example, the ferrous b-hemes in the homologous cyt bc 1 complex have been found to undergo efficient photo-dissociation and -oxidation within femtoseconds after visible light excitation. 11 While photodissociation seems to be a rather standard feature in hemeembedded proteins, 9, 12 the initiation of a charge separated state is intriguing within a complex that is directly involved in cross-membrane proton-coupled-electron transfer. 1 The cyt b 6 f complex, as part of the photosynthetic pathway, is naturally exposed to sun light.…”