Viscosity Dependence of the Electron Transfer Rate from Bound Cytochromecto P840 in the Photosynthetic Reaction Center of the Green Sulfur BacteriumChlorobium tepidum,

Oh‐oka, Hirozo; Iwaki, Masayo; Itoh, Shigeru

doi:10.1021/bi9701787

Cited by 55 publications

(62 citation statements)

References 37 publications

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“…The equation (17) and Fig.1 show that the distribution ρ(q) is zero above the critical value of the weight q c = 0.5 given by (15). We conclude that the contribution from cosolvent molecules into the viscosity for the movement of the system along the reaction coordinate ζ/η 0 can not enter with the weight greater that one half of that from protein matrix and solvent molecules to be compatible with observations expressed by (1).…”

Section: Discussionsupporting

confidence: 73%

“…There seems to be consensus among researches that the effect of solvent viscosity on the enzymatic reaction is mediated by protein dynamics [2], [3], [5], [6], [8], [9], [10], [11], [12], [15]. That is why we further identify the viscosity for the movement of the system along the reaction coordinate with the viscosity at relevant motion for catalysis of individual fragments in protein interior and in enzyme active site.…”

Section: Introductionmentioning

confidence: 98%

“…Viscosity dependence of enzymatic and protein (ligand binding/rebinding) reactions is a long standing problem for biophysics [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. For such reactions the functional dependence of the reaction rate constant for the rate limiting stage k on solvent viscosity η has the form…”

Section: Introductionmentioning

confidence: 99%

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Model for solvent viscosity effect on enzymatic reactions

Sitnitsky

2010

Chemical Physics

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Why reaction rate constants for enzymatic reactions are typically inversely proportional to fractional power exponents of solvent viscosity remains to be already a thirty years old puzzle. Available interpretations of the phenomenon have not led to consensus among researches about its origin. They invoke to either a modification of 1. the conventional Kramers' theory or that of 2. the Stokes law. We show that there is an alternative interpretation of the phenomenon at which neither of these modifications is in fact indispensable. Basing on an analogy from the theory of adsorption on heterogeneous surfaces we reconcile 1. and 2. with the experimentally observable dependence. We assume that an enzyme solution in solvent with or without cosolvent molecules is an ensemble of samples with different values of the viscosity for the movement of the system along the reaction coordinate. We assume that this viscosity consists of the contribution with the weight q from cosolvent molecules and that with the weight 1− q from protein matrix and solvent molecules. We introduce heterogeneity in our system with the help of a distribution over the weight q. The function of the distribution is a unique characteristic of the solution of enzymes (type of the enzyme, cosolvent molecular weight, pH, temperature, etc.). We verify the obtained solution of the integral equation for the unknown function of the distribution by direct substitution. We conclude that even at linear relationship between the solvent viscosity and that for the movement of the system along the reaction coordinate our approach enables us to obtain the required dependence. All parameters of the model are related to experimentally observable values. The meaning of fractional exponents appears to be the characteristic for the behavior of the distribution with the variation of the weight q. Our approach yields the existence of the limit value for the fractional power exponent with the decrease of cosolvent molecular weight that is in agreement experimental data known from the literature. This limit value is determined by the properties of the protein structure and thus is a unique characteristic of the type of the enzyme only rather than that of the solution. General formalism is exemplified by the analysis of literature experimental data for oxygen escape from hemerythin.

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Section: Discussionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Model for solvent viscosity effect on enzymatic reactions

Sitnitsky

2010

Chemical Physics

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“…Preparation of the RC Complex and SDS-PAGE-The RC complex was isolated from the wild-type and mutant cells as described previously by Oh-oka et al (27). All procedures for the preparation were carried out under anaerobic conditions in a chamber (Coy Laboratory Products, Ann Arbor, MI).…”

Section: Methodsmentioning

confidence: 99%

Function of a PscD Subunit in a Homodimeric Reaction Center Complex of the Photosynthetic Green Sulfur Bacterium Chlorobium tepidum Studied by Insertional Gene Inactivation

Tsukatani

Miyamoto

Itoh

et al. 2004

Journal of Biological Chemistry

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The PscD subunit in the homodimeric "type I" photosynthetic reaction center (RC) complex of the green sulfur bacterium Chlorobium tepidum was disrupted by insertional mutagenesis of its relevant pscD gene. This is the first report on the use of the direct mutagenic approach into the RC-related genes in green sulfur bacteria. The RC complex of C. tepidum is supposed to form a homodimer of two identical PscA subunits together with three other subunits: PscB (F A /F B -containing protein), PscC (cytochrome c z ), and PscD. PscD shows a relatively low but significant similarity in its amino acid sequence to PsaD in the photosystem I of plants and cyanobacteria. We studied the biochemical and spectroscopic properties of a mutant lacking PscD in order to elucidate its unknown function. 1) The RC complex isolated from the mutant cells showed no band corresponding to PscD on SDS-PAGE analysis. 2) The growth rate of the PscD-less mutant was slower than that of the wildtype cells at low light intensities. 3) Time-resolved fluorescence spectra at 77 K revealed prolonged decay times of the fluorescence from bacteriochlorophyll c on the antenna chlorosome and from bacteriochlorophyll a on the Fenna-Matthews-Olson antenna protein in the mutant cells. The loss of PscD led to a much slower energy transfer from the antenna pigments to the special pair bacteriochlorophyll a (P840). 4) The mutant strain exhibited slightly less activity of ferredoxin-mediated NADP ؉ photoreduction compared with that in the wild-type strain. The extent of suppression, however, was less significant than that reported in the PsaD-less mutants of cyanobacterial photosystem I. The evolutionary relationship between PscD and PsaD was also discussed based on a structural homology modeling of the former.Photosynthetic organisms convert light energy into electrochemical free energy by carrying out a series of light-driven electron transfer reactions. This process, which is fundamental for life, is mediated by reaction center (RC) 1 complexes. The RCs are primarily grouped into two types based on their terminal electron acceptors, type I (FeS-type) RCs and type II (quinone-type) RCs. Purple photosynthetic bacteria contain only type II RCs, which do not evolve oxygen, whereas oxygenic cyanobacteria and plants utilize both type I (photosystem I) and type II (photosystem II) RCs, which are connected in-line through the b 6 f complex. Green sulfur bacteria and heliobacteria have unique type I RCs, so-called "homodimeric" RCs, which are made of two identical core polypeptides.The "heterodimeric" type I and II RCs, which are found in all photosynthetic organisms other than green sulfur bacteria and heliobacteria, consist of a set of two partially different core polypeptides that produce a slightly asymmetric arrangement of cofactors. A three-dimensional structure of the heterodimeric RC was first obtained from the type II RC of the purple bacterium Blastochloris viridis in 1985 (1). Recently, those of photosystem I and II RCs from the thermophilic cyanobacterium Sy...

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“…The Ca. C. thermophilum genome does not encode PscC, the c-type cytochrome that donates electrons to the primary donor (11,12), or PscD, a protein that may enhance electron transfer from the F A /F B clusters of PscB to ferredoxin (13) in the RCs of GSB. Time course metatranscriptome profiling studies over a diel cycle have demonstrated that the transcripts for the pscA gene are least abundant during the day when the microbial mats are oxic, but pscA transcripts are highest during the late afternoon and evening when the mats are anoxic (14).…”

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confidence: 99%