Proton-coupled electron transfer at the Qo-site of the bc1 complex controls the rate of ubihydroquinone oxidation

AbstractThe rate-limiting reaction of the bc1 complex from Rhodobacter sphaeroides is transfer of the first electron from ubihydroquinone (quinol, QH2) to the [2Fe–2S] cluster of the Rieske iron–sulfur protein (ISP) at the Qo-site. Formation of the ES-complex requires participation of two substrates (S), QH2 and ISPox. From the variation of rate with [S], the binding constants for both substrates involved in formation of the complex can be estimated. The configuration of the ES-complex likely involves the dissociated form of the oxidized ISP (ISPox) docked at the b-interface on cyt b, in a complex in which Nε of His-161 (bovine sequence) forms a H-bond with the quinol OH. A coupled proton and electron transfer occurs along this H-bond. This brief review discusses the information available on the nature of this reaction from kinetic, structural and mutagenesis studies. The rate is much slower than expected from the distance involved, likely because it is controlled by the low probability of finding the proton in the configuration required for electron transfer. A simplified treatment of the activation barrier is developed in terms of a probability function determined by the Brønsted relationship, and a Marcus treatment of the electron transfer step. Incorporation of this relationship into a computer model allows exploration of the energy landscape. A set of parameters including reasonable values for activation energy, reorganization energy, distances between reactants, and driving forces, all consistent with experimental data, explains why the rate is slow, and accounts for the altered kinetics in mutant strains in which the driving force and energy profile are modified by changes in Em and/or pK of ISP or heme bL

Donor-side photoinhibition in photosystem II from Chlamydomonas reinhardtii upon mutation of tyrosine-Z in the D1 polypeptide to phenylalanine

AbstractWhen tyrosine-Z of the D1-polypeptide of the photosystem II from Chlamydomonas reinhardtii was changed to phenylalanine, the rapid donor to P680+ was lost, and P680+ accumulated on illumination. The rapid donation from tyrosine-Z was replaced by a slow electron transfer from an endogenous donor. Spectrophotometric measurements showed that carotenoids and chlorophylls were bleached by the P680+ either directly or indirectly upon illumination. The carotenoid bleaching was inhibited in the presence of SOD or catalase, but the reaction did not require molecular oxygen as an electron acceptor. These observations led us to conclude that active oxygen radicals, possibly hydroxyl radicals, take part in the destruction of carotenoids in the Y161F mutant. Possible mechanisms for the destruction are discussed

In Situ Kinetics of Cytochromes

ABSTRACT: In Rhodobacter sphaeroides chromatophores, cytochromes (cyt) c 1 and c 2 have closely overlapping spectra, and their spectral deconvolution provides a challenging task. As a result, analyses of the kinetics of different cytochrome components of the bc 1 complex in purple bacteria usually report only the sum cyt c 1 + cyt c 2 kinetics. Here we used newly determined difference spectra of individual components to resolve the kinetics of cyt c 1 and c 2 in situ via a least-squares (LS) deconvolution. We found that the kinetics of cyt c 1 and c 2 are significantly different from those measured using the traditional difference wavelength (DW) approach, based on the difference in the absorbance at two different wavelengths specific for each component. In particular, with the wavelength pairs previously recommended, differences in instrumental calibration led to kinetics of flash-induced cyt c 1 oxidation measured with the DW method which were faster than those determined by the LS method (half-time of ∼120 µs vs half-time of ∼235 µs, in the presence of antimycin). In addition, the LS approach revealed a delay of ∼50 µs in the kinetics of cyt c 1 oxidation, which was masked when the DW approach was used. We attribute this delay to all processes leading to the oxidation of cyt c 1 after light activation of the photosynthetic reaction center, especially the dissociation of cyt c 2 from the reaction center. We also found that kinetics of both cyt c 1 and c 2 measured by the DW approach were significantly distorted at times longer than 1 ms, due to spectral contamination from changes in the b hemes. The successful spectral deconvolution of cyt c 1 and c 2 , and inclusion of both cytochromes in the kinetic analysis, significantly increase the data available for mechanistic understanding of bc 1 turnover in situ

In photosynthesis, oxygen comes from water: from a 1787 book for women by Monsieur De Fourcroy

Abstract It is now well established that the source of oxygen in photosynthesis is water. The earliest suggestion previously known to us had come from René Bernard Wurmser (1930). Here, we highlight an earlier report by Monsieur De Fourcroy (1787), who had already discussed the broad outlines of such a hypothesis in a book on Chemistry written for women. We present here a free translation of a passage from this book, with the original text in French as an Appendix

CSF1R inhibitor JNJ-40346527 attenuates microglial proliferation and neurodegeneration in P301S mice

Neuroinflammation and microglial activation are significant processes in Alzheimer’s disease pathology. Recent genome-wide association studies have highlighted multiple immune-related genes in association with Alzheimer’s disease, and experimental data have demonstrated microglial proliferation as a significant component of the neuropathology. In this study, we tested the efficacy of the selective CSF1R inhibitor JNJ-40346527 (JNJ-527) in the P301S mouse tauopathy model. We first demonstrated the anti-proliferative effects of JNJ-527 on microglia in the ME7 prion model, and its impact on the inflammatory profile, and provided potential CNS biomarkers for clinical investigation with the compound, including pharmacokinetic/pharmacodynamics and efficacy assessment by TSPO autoradiography and CSF proteomics. Then, we showed for the first time that blockade of microglial proliferation and modification of microglial phenotype leads to an attenuation of tau-induced neurodegeneration and results in functional improvement in P301S mice. Overall, this work strongly supports the potential for inhibition of CSF1R as a target for the treatment of Alzheimer’s disease and other tau-mediated neurodegenerative diseases

Inflammatory biomarkers in Alzheimer's disease plasma

Introduction:Plasma biomarkers for Alzheimer’s disease (AD) diagnosis/stratification are a“Holy Grail” of AD research and intensively sought; however, there are no well-established plasmamarkers.Methods:A hypothesis-led plasma biomarker search was conducted in the context of internationalmulticenter studies. The discovery phase measured 53 inflammatory proteins in elderly control (CTL;259), mild cognitive impairment (MCI; 199), and AD (262) subjects from AddNeuroMed.Results:Ten analytes showed significant intergroup differences. Logistic regression identified five(FB, FH, sCR1, MCP-1, eotaxin-1) that, age/APOε4 adjusted, optimally differentiated AD andCTL (AUC: 0.79), and three (sCR1, MCP-1, eotaxin-1) that optimally differentiated AD and MCI(AUC: 0.74). These models replicated in an independent cohort (EMIF; AUC 0.81 and 0.67). Twoanalytes (FB, FH) plus age predicted MCI progression to AD (AUC: 0.71).Discussion:Plasma markers of inflammation and complement dysregulation support diagnosis andoutcome prediction in AD and MCI. Further replication is needed before clinical translatio

Kinetics of the oxidation—reduction reactions of the photosystem II quinone acceptor complex, and the pathway for deactivation

AbstractWhen the photosystem II quinone acceptor complex has been singly reduced to the state QAQ−B, there is a 22 s half-time back-reaction of Q−B with an oxidized photosystem II donor (S2), directly measured here for the first time. From the back-reaction kinetics with and without inhibitors, kinetic and equilibrium parameters have been estimated. We suggest that the state QAQ−B of the complex is formed by a second-order reaction of vacant reaction centers in the state Q−A with plastoquinone from the pool, and discuss the physico-chemical parameters involved