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Biomedical subjects

C C Moser

Publications and source records attributed to C C Moser.

26 records · Page 2Linked to original sources
PubMed1994

Femtosecond coherent transient infrared spectroscopy of reaction centers from Rhodobacter sphaeroides.

Protein and cofactor vibrational dynamics associated with photoexcitation and charge separation in the photosynthetic reaction center were investigated with femto-second (300-400 fs) time-resolved infrared (1560-1960 cm-1) spectroscopy. The experiments are in the coherent transient limit where the quantum uncertainty principle governs the evolution of the protein vibrational changes. No significant protein relaxation accompanies charge separation, although the electric field resulting from charge separation modifies the polypeptide carbonyl spectra. The potential energy surfaces of the "special pair" P and the photoexcited singlet state P* and environmental perturbations on them are similar as judged from coherence transfer measurements. The vibrational dephasing time of P* modes in this region is 600 fs. A subpicosecond transient at 1665 cm-1 was found to have the kinetics expected for a sequential electron transfer process. Kinetic signatures of all other transient intermediates, P, P*, and P+, participating in the primary steps of photosynthesis were identified in the difference infrared spectra.

Kinetics↗
PubMed1994

Design and synthesis of multi-haem proteins.

A water-soluble, 62-residue, di-alpha-helical peptide has been synthesized which accommodates two bis-histidyl haem groups. The peptide assembles into a four-helix dimer with 2-fold symmetry and four parallel haems that closely resemble native haems in their spectral and electrochemical properties, including haem-haem redox interaction. This protein is an essential intermediate in the synthesis of molecular 'maquettes', a novel class of simplified versions of the metalloproteins involved in redox catalysis and in energy conversion in respiratory and photosynthetic electron transfer.

Amino Acid Sequence↗
PubMed1993

Picosecond infrared studies of the dynamics of the photosynthetic reaction center.

The changes in the vibrational transitions of the protein and redox cofactors of the photosynthetic reaction center were examined by picosecond infrared spectroscopy. The spectra in the vibrational mid-infrared region (1800-1550 cm-1) of hydrated and partially dehydrated reaction centers were investigated from 50 ps to 4 ns after photoinitiation of the electron transfer. Features in the infrared difference spectra were identified with both protein and redox cofactor vibrational modes and correlated with electron transfer events whose kinetics were measured in the infrared and visible regions. The observed protein response is confined to a few amide I transitions (1644 cm-1, 1661 cm-1, 1665 cm-1) and carboxylic residues (1727 cm-1). About 85% of the observed signal corresponded to alterations in the cofactor-associated ester and keto carbonyls. The amide I and carboxylic transitions appeared prior to 50 ps, suggesting that the primary electron transfer event is coupled with a specific piece of the protein backbone and to glutamic or aspartic residues nearby the special pair. Infrared absorption changes accompanying bacteriochlorophyll-dimer cation formation dominated the signal at all times investigated. Infrared spectral changes observed in hydrated and partially dehydrated reaction centers were distinctly different; a band at 1665 cm-1 with a spectral width of 6 cm-1 in the hydrated protein, corresponding to a protein amide I bleach, was not present in the dehydrated film. These differences are discussed in terms of the markedly different electron transfer kinetics observed in the presence of water.

Electron Transport↗
PubMed1992

Engineering protein structure for electron transfer function in photosynthetic reaction centers.

A basic relationship is defined that incorporates the three parameters that effectively modulate the rate of intraprotein electron transfer, namely distance, free energy and reorganization energy. This empirically validated relationship is used to explore the minimal requirements for protein-catalyzed conversion of excited electronic states into stable charge separated states, the essence of photosynthesis.

Electron Transport↗
PubMed1992

Nature of biological electron transfer.

Powerful first-order analysis of intraprotein electron transfer is developed from electron-transfer measurements both in biological and in chemical systems. A variation of 20 A in the distance between donors and acceptors in protein changes the electron-transfer rate by 10(12)-fold. Protein presents a uniform electronic barrier to electron tunnelling and a uniform nuclear characteristic frequency, properties similar to an organic glass. Selection of distance, free energy and reorganization energy are sufficient to define rate and directional specificity of biological electron transfer, meeting physiological requirements in diverse systems.

Animals↗
PubMed1988

Cytochrome c and c2 binding dynamics and electron transfer with photosynthetic reaction center protein and other integral membrane redox proteins.

To further the understanding of the details of c-type cytochrome action as a redox carrier between major electron-transfer proteins, the single-turnover kinetics time course of cytochrome c and cytochrome c2 oxidation by flash-activated photosynthetic reaction center (purified from the bacterium Rhodobacter sphaeroides) has been examined under a wide variety of conditions of concentration, ionic strength, and viscosity with reaction center present in detergent dispersion and phosphatidylcholine proteoliposomes. We find that the three-state model proposed by Overfield and Wraight [Overfield, R. E., & Wraight, C. A. (1980) Biochemistry 19, 3322-3327] is generally sufficient to model the kinetics time course; many similarities are found with the cytochrome c-cytochrome c oxidase interaction in mitochondria. Further, we find the following: (1) Significant "product inhibition" by oxidized cytochrome c (c2) bound to the reaction center is apparent. (2) The viscosity sensitivity of the electron transfer into the reaction center from bound cytochrome c (c2) suggests a physical interpretation of the distal state. (3) The exchange dynamics of oxidized and reduced cytochrome c (c2) are similar regardless of the state of activation of the reaction center. (4) Preferential binding of the oxidized form of cytochrome c is revealed upon reconstitution of the reaction center into neutral lipid vesicles, permitting an independent confirmation of the binding suggested by the kinetics. (5) Flash-activated electron-transfer kinetics in reaction center hybrid protein systems have shown that diffusion and competitive binding characterize the behavior of cytochrome c as a redox carrier between the reaction center protein and either the cytochrome bc1 complex or the cytochrome c oxidase.

Bacterial Proteins↗
PubMed1984

Two distinct quinone-modulated modes of antimycin-sensitive cytochrome b reduction in the cytochrome bc1 complex.

Reduction of cytochrome b-560 (analogous to cyt b-562 of mitochondria) via an antimycin-sensitive route has been revealed in chromatophores of the photosynthetic bacterium, Rhodopseudomonas sphaeroides Ga. Indeed, the results suggest that two reductive mechanisms can be operative. One is consistent with the idea that the quinol generated at the reaction center QB site enters the Q pool and, via the Qc site, equilibrates with cytochrome b-560. The other reductive mode circumvents redox equilibrium with the pool; we consider that this could result from a direct encounter of the reaction center with the bc1 complex perhaps involving a direct QB-Qc site interaction. This latter reaction is suppressed by occupancy of the Qc site, not only by antimycin but by ubiquinol and ubiquinone.

Antimycin A↗