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At least 739 records · Page 41Linked to original sources
PubMed2001

A simple mediatorless amperometric method using the cyanobacterium Synechococcus leopoliensis for the detection of phytotoxic pollutants.

The unicellular cyanobacterium Synechoccocus leopoliensis is used in a micro-electrochemical cell to generate photocurrents. The photocurrent is dependent on photosynthetic electron transport and is mediated by hydrogen peroxide formation following the reduction of oxygen on the acceptor side of photosystem I. This is the first known application of cyanobacteria in an electrochemical device where no artificial electroactive mediator is needed. The potential for the development of this micro-electrochemical cell for the detection of phytotoxic pollutants, such as herbicides and toxic metal cations, using the photosynthetic system of the cyanobacteria without interference from added electron acceptor is discussed.

Cyanobacteria↗
PubMed1992

Core mutations of Synechococcus sp. PCC 7002 phycobilisomes: a spectroscopic study.

Three cyanobacterial strains harboring mutations affecting phycobilisome (PBS) cores were studied using steady state absorption and fluorescence and time-resolved fluorescence. The apcF mutant, missing beta 18, and the apcDF mutant, missing both alpha APB and beta 18, showed only small spectroscopic differences from the wild-type strain; their PBS emission was blue shifted by 10 nm, whereas their absorption spectra and time-resolved fluorescence kinetics were virtually unchanged. The third mutant studied was the apcE/C186S mutant in which the chromophore-binding cysteine-186 in the LCM99 polypeptide has been substituted with serine. The apcE/C186S mutant contained a modified chromophore which significantly changed the spectroscopic properties of the PBS complex. The apcE/C186S PBS absorbed more than the wild-type strain at 705 nm, and the emission spectrum gave two peaks at 660 nm and 715 nm. The time-resolved kinetics of the apcE/C186S mutant PBS were also significantly altered from those of the wild-type strain.

Cyanobacteria↗
PubMed2003

Energy transfer in photosystem I of cyanobacteria Synechococcus elongatus: model study with structure-based semi-empirical Hamiltonian and experimental spectral density.

We model the energy transfer and trapping kinetics in PSI. Rather than simply applying Förster theory, we develop a new approach to self-consistently describe energy transfer in a complex with heterogeneous couplings. Experimentally determined spectral densities are employed to calculate the energy transfer rates. The absorption spectrum and fluorescence decay time components of the complex at room temperature were reasonably reproduced. The roles of the special chlorophylls (red, linker, and reaction center, respectively) molecules are discussed. A formally exact expression for the trapping time is derived in terms of the intrinsic trapping time, mean first passage time to trap, and detrapping time. The energy transfer mechanism is discussed and the slowest steps of the arrival at the primary electron donor are found to contain two dominant steps: transfer-to-reaction-center, and transfer-to-trap-from-reaction-center. The intrinsic charge transfer time is estimated to be 0.8 approximately 1.7 ps. The optimality with respect to the trapping time of the calculated transition energies and the orientation of Chls is discussed.

Computer Simulation↗
PubMed2002

Truncated hemoglobin from the cyanobacterium Synechococcus sp. PCC 7002: evidence for hexacoordination and covalent adduct formation in the ferric recombinant protein.

The glbN gene for the hemoglobin of Synechoccocus sp. PCC 7002, a cyanobacterium incapable of nitrogen fixation, was cloned and overexpressed in Escherichia coli. The 123-residue protein was purified from inclusion bodies and reconstituted with iron protoporphyrin IX to obtain the ferric form of the holoprotein. Mass spectrometric analysis confirmed the identity of the polypeptide. NMR and optical data demonstrated that the protein so prepared contained a hexacoordinate heme group, as observed in the related globin from Synechocystis sp. PCC 6803 [Scott, N. L., and Lecomte, J. T. J. (2000) Protein Sci. 9, 587-597]. The data were consistent with a similar bis-histidine coordination scheme involving His46 (E10) on the distal side and His70 (F8) on the proximal side. Several aromatic residues were identified in the vicinity of the heme and were used to establish the orientation of the prosthetic group in the polypeptide matrix. In this protein, as in that from Synechocystis sp. PCC 6803, there was a marked preference for the heme orientation in which pyrroles C and D contact the C-E corner of the protein. Both hemoglobins were found capable of forming a product in which the heme is cross-linked to the polypeptide through modification of a vinyl group.

Amino Acid Sequence↗
PubMed1997

Characterization of the unbound 2[Fe4S4]-ferredoxin-like photosystem I subunit PsaC from the Cyanobacterium synechococcus elongatus.

Recombinant PsaC was reconstituted in vitro and investigated by UV/vis, EPR, and 1H NMR spectroscopy. Its UV/vis and EPR spectroscopic properties correspond to those of the wild-type protein. Fast repetition 1D and 2D 1H NMR spectra allowed the sequence-specific assignment of the hyperfine-shifted proton resonances of the cluster-ligating resonances, taking advantage also of chemical shift analogies with other 4 and 8 Fe ferredoxins and a structural model for PsaC. The Calpha-Cbeta-S-Fe dihedral angles of the cluster ligands could be estimated from the chemical shifts and relaxation properties of their betaCH2 protons. All NMR-derived structural information on PsaC confirms its similarity to smaller 8Fe ferredoxins serving as electron transfer proteins in solution. Partial reduction of PsaC leads to an intermediate species with strongly exchange broadened 1H NMR resonances. The intermolecular electron exchange rate is estimated to be in the 10(2)-10(4) s-1 range, the intramolecular electron exchange rate between the two [Fe4S4] clusters to be higher than 10(4) s-1. The consequences of these findings for the electron transfer in photosystem I are discussed.

Cyanobacteria↗
PubMed1998

Transient-state kinetic analysis of Synechococcus glutamate 1-semialdehyde aminotransferase.

We report a transient-state kinetic analysis relating to the mechanism of glutamate 1-semialdehyde aminotransferase (GSAT). Multiple-wavelength spectral kinetic data were collected by micro-stopped-flow spectrophotometry. Time resolved spectral sketches resulting from reactions with glutamate 1-semialdehyde (GSA), 4,5-diaminovalerate (DAVA), and 5-aminolevulinate (ALA) indicated various transient chromophoric intermediates. On the basis of the generally accepted mechanism of other aminotransferases and absorbance characteristics of associated intermediates, these transient chromophores are likely associated with Schiff base formation, ketimine/aldimine tautomerization, and transimidation etc. Spectral kinetic changes associated with these putative intermediates were, in general, concentration dependent. Various experimental evidence, including reactions with the GSAT lys272ile mutant, suggested rapid equilibrium of isomeric aldimines and geminal diamines. With this and related simplifying assumptions, a minimal mechanism was derived which provided a means for transient-state spectral kinetic analysis of reactions with GSA, DAVA, and ALA, all of which lead to the formation of the same putative central enzyme complex. Resulting kinetic constants were internally consistent, in general agreement with steady-state and equilibrium data (KM, kcat, and Keq), and provided the basis for a reasonable computer simulation of the original data set (variance approximately 4 x 10(-5)). Reequilibration of enzyme intermediates following an apparent pseudoequilibrium indicated thermodynamically driven dissociation of the central aldiminic enzyme complex. This is consistent with previous observations and the minimal mechanism used in this kinetic analysis and suggests a plausible regulatory mechanism of GSAT.

Amino Acids, Diamino↗