On the appearance of chaos in a model of the Belousov reaction

Summary A modified version of the Oregonator is analysed as a model of oscillations, bistability and chaos in the bromate-malonic acid-cerium reaction.This study was supported by the National Cancer Institute, USA, Grant No. 5 F32 CAO5152-02.     

P+HA- charge recombination reaction rate constant in Rhodobacter sphaeroides reaction centers is independent of the P/P+ midpoint potential.

The kinetics of the P+HA- (oxidized donor, reduced bacteriopheophytin acceptor) recombination reaction was measured in a series of reaction center mutants of Rhodobacter sphaeroides with altered P/P+ midpoint potentials between 410 and 765 mV. The time constant for P+HA- recombination was found to range between 14 and 26 ns and was essentially independent of P/P+ midpoint potential. Previous work has shown that the time constant for initial electron transfer in these mutants at room temperature is also only weakly dependent on the P/P+ midpoint potential, ranging from about 2.5 ps to about 50 ps. These results, taken together, imply that heterogeneity in the P/P+ midpoint potential within the reaction center population is not likely the dominant cause of the substantial kinetic complexity observed in the decay of the excited singlet state of P on the picosecond to nanosecond time scale. In addition, the pathway of P+HA- decay appears to be direct or via P+BA- rather than proceeding back through P, even in the highest-potential mutant, as is evident from the fact that the rate of P+HA- recombination is unaltered by pushing P+HA- much closer to P in energy. Finally, the midpoint potential independence of the P+HA- recombination rate constant suggests that the slow rate of P+HA- recombination arises from an inherent limitation in the maximum rate of this process rather than because it occurs in the inverted region of a classical Marcus rate vs free energy curve.     

The study of the state [P870 B800] in bacterial reaction centers by selective picosecond and low-temperature spectroscopies

The selective picosecond excitation of Rhodopseudomonas sphaeroides (R-26) reaction centers (RCs) at 870 nm induces the formation of the transient state within <1 ps followed by the conversion into the state P^F (P^± Bph^±− during 7 ± 2 ps at both 293 K and 110 K. The transient state including the intense bleaching at 800 nm has been shown not to be due: (a) to photon excitation at 870 nm; (b) the excitation of P⁺; (c) photoselection effects. The transient state is interpreted as the state ¹[P⁺B⁻] in agreement with earlier works. The primary formation of the state ¹P⁺B⁻] and the big effective singlet-triplet splitting in this state correspond to the spectral splitting of the P band at 900 nm in R-26 RCs and at 1000 nm in Rhodopseudomonas viridis RCs found at 4.2 K and attributed to the optical transition to both ¹P and ¹[P⁺B⁻] states.     

The site-directed mutation I(L177)H in Rhodobacter sphaeroides reaction center affects coordination of P(A) and B(B) bacteriochlorophylls

To explore the influence of the I(L177)H single mutation on the properties of the nearest bacteriochlorophylls (BChls), three reaction centers (RCs) bearing double mutations were constructed in the photosynthetic purple bacterium Rhodobacter sphaeroides, and their properties and pigment content were compared with those of the correspondent single mutant RCs. Each pair of the mutations comprised the amino acid substitution I(L177)H and another mutation altering histidine ligand of BChl P(A) or BChl B(B). Contrary to expectations, the double mutation I(L177)H+H(L173)L does not bring about a heterodimer RC but causes a 46nm blue shift of the long-wavelength P absorbance band. The histidine L177 or a water molecule were suggested as putative ligands for P(A) in the RC I(L177)H+H(L173)L although this would imply a reorientation of the His backbone and additional rearrangements in the primary donor environment or even a repositioning of the BChl dimer. The crystal structure of the mutant I(L177)H reaction center determined to a resolution of 2.9? shows changes at the interface region between the BChl P(A) and the monomeric BChl B(B). Spectral and pigment analysis provided evidence for β-coordination of the BChl B(B) in the double mutant RC I(L177)H+H(M182)L and for its hexacoordination in the mutant reaction center I(L177)H. Computer modeling suggests involvement of two water molecules in the β-coordination of the BChl B(B). Possible structural consequences of the L177 mutation affecting the coordination of the two BChls P(A) and B(B) are discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Raphael Meldola,his blue and his times

Raphael Meldola (1849–1915), English industrial and academic chemist, spectroscopist, naturalist, educator and lobbyist for science, is today almost a forgotten scientist whose life is celebrated only with a medal awarded by the Royal Society of Chemistry that honors achievement by younger chemists. In the 1870–80s, however, he invented a number of important synthetic dyestuffs including the cotton dyes isamine blue and Meldola's blue, and also naphthol green B, all of which have had application in biology and medicine. I describe here the early emergence of the synthetic dye industry, the first science-based industry, Meldola's role in its development, and his own inventions. Meldola's wide ranging achievements in science led to appointments as president of important professional scientific and manufacturers' societies. He was a fervent disciple of natural selection, a correspondent of Charles Darwin, and a prominent 19^th-century neo-Darwinian. In 1886, drawing on analogies with evolutionary theory, he warned the British that neglect of science, particularly chemistry, would lead to industrial decline and even extinction, though his message generally was ignored, at least until 1914.     

Raphael Meldola, his blue and his times

Raphael Meldola (1849-1915), English industrial and academic chemist, spectroscopist, naturalist, educator and lobbyist for science, is today almost a forgotten scientist whose life is celebrated only with a medal awarded by the Royal Society of Chemistry that honors achievement by younger chemists. In the 1870-80s, however, he invented a number of important synthetic dyestuffs including the cotton dyes isamine blue and Meldola's blue, and also naphthol green B, all of which have had application in biology and medicine. I describe here the early emergence of the synthetic dye industry, the first science-based industry, Meldola's role in its development, and his own inventions. Meldola's wide ranging achievements in science led to appointments as president of important professional scientific and manufacturers' societies. He was a fervent disciple of natural selection, a correspondent of Charles Darwin, and a prominent 19(th)-century neo-Darwinian. In 1886, drawing on analogies with evolutionary theory, he warned the British that neglect of science, particularly chemistry, would lead to industrial decline and even extinction, though his message generally was ignored, at least until 1914.     

Spectroscopic features of cytochrome P450 reaction intermediates

Cytochromes P450 constitute a broad class of heme monooxygenase enzymes with more than 11,500 isozymes which have been identified in organisms from all biological kingdoms [1]. These enzymes are responsible for catalyzing dozens chemical oxidative transformations such as hydroxylation, epoxidation, N-demethylation, etc., with very broad range of substrates [2] and [3]. Historically these enzymes received their name from ‘pigment 450’ due to the unusual position of the Soret band in UV–vis absorption spectra of the reduced CO-saturated state [4] and [5]. Despite detailed biochemical characterization of many isozymes, as well as later discoveries of other ‘P450-like heme enzymes’ such as nitric oxide synthase and chloroperoxidase, the phenomenological term ‘cytochrome P450’ is still commonly used as indicating an essential spectroscopic feature of the functionally active protein which is now known to be due to the presence of a thiolate ligand to the heme iron [6]. Heme proteins with an imidazole ligand such as myoglobin and hemoglobin as well as an inactive form of P450 are characterized by Soret maxima at 420 nm [7]. This historical perspective highlights the importance of spectroscopic methods for biochemical studies in general, and especially for heme enzymes, where the presence of the heme iron and porphyrin macrocycle provides rich variety of specific spectroscopic markers available for monitoring chemical transformations and transitions between active intermediates of catalytic cycle.     

31P NMR spin-transfer in the phosphoglyceromutase reaction

The rate of exchange of phosphoryl groups between 2- and 3-phosphoglycerate catalysed by (a) high concentrations (approximately equal to 5.0 mg protein ml-1) of rabbit muscle phosphoglyceromutase and (b) lysed human erythrocytes was measured using saturation and inversion transfer techniques with 31P-NMR spectroscopy. This is the first reported application of these techniques to a study of this particular enzymic reaction either in vitro or in situ in a cell cytosol. Selective irradiation of resonances was achieved by the DANTE pulse sequence which had not previously been used for spin-transfer studies. New equilibrium exchange theory was developed for the simplest model of a two-reactant enzyme-catalysed reaction and this was used to calculate turnover rates for the enzymes. There was a close similarity between the turnover rates calculated from the spin-transfer data obtained from the systems in vitro and in situ and those obtained by conventional enzymic assays, at low enzyme concentrations. This suggested an absence of any homogeneous enzyme-enzyme interactions which modify the kinetics at high protein concentrations either in lysates or in the system in vitro.     

B cell complement receptor 2 transfer reaction

The B cell C receptor specific for C3dg (CR2) shares a number of features with the primate E C receptor (CR1). Previously, we have demonstrated, both in vitro and in animal models, that immune complexes (IC) bound to primate E CR1, either via C opsonization or by means of bispecific mAb complexes, can be transferred to acceptor macrophages in a process that also removes CR1 from the E. We have now extended this paradigm, the transfer reaction, to include B cell CR2. We used both flow cytometry and fluorescence microscopy to demonstrate that IC bound to Raji cell CR2, either via C opsonization or through the use of an anti-CR2 mAb, are transferred to acceptor THP-1 cells. This reaction, which appears to require Fc recognition of IgG bound to Raji cell CR2, also leads to transfer of CR2. Additional support for the B cell transfer reaction is provided in a prototype study in a monkey model in which IC bound to B cell CR2 are localized to the spleen. These findings may have important implications with respect to defining the role of C in IC handling during the normal immune response.     

TiO2 Band Restructuring by B and P Dopants

An examination of the effect of B- and P-doping and codoping on the electronic structure of anatase TiO₂ by performing density functional theory calculations revealed the following: (i) B- or P-doping effects are similar to atomic undercoordination effects on local bond relaxation and core electron entrapment; (ii) the locally entrapped charge adds impurity levels within the band gap that could enhance the utilization of TiO₂ to absorb visible light and prolong the carrier lifetime; (iii) the core electron entrapment polarizes nonbonding electrons in the upper edges of the valence and conduction bands, which reduces not only the work function but also the band gap; and (iv) work function reduction enhances the reactivity of the carriers and band gap reduction promotes visible-light absorption. These observations may shed light on effective catalyst design and synthesis.