Mössbauer and EPR study of recombinant acetyl-CoA synthase from Moorella thermoacetica.

Mössbauer and EPR spectroscopies were used to study the electronic structure of the A-cluster from recombinant acetyl-CoA synthase (the alpha subunit of the alpha2beta2 acetyl-CoA synthase/CO dehydrogenase). Once activated with Ni, these subunits have properties mimicking those associated with the alpha2beta2 tetramer, including structural heterogeneities. The Fe4S4 portion of the A-cluster in oxidized, methylated, and acetylated states was in the 2+ core oxidation state.

LdpA: a component of the circadian clock senses redox state of the cell.

The endogenous 24-h (circadian) rhythms exhibited by the cyanobacterium Synechococcus elongatus PCC 7942 and other organisms are entrained by a variety of environmental factors. In cyanobacteria, the mechanism that transduces environmental input signals to the central oscillator of the clock is not known. An earlier study identified ldpA as a gene involved in light-dependent modulation of the circadian period, and a candidate member of a clock-entraining input pathway.

Effect of Zn on acetyl coenzyme a synthase: evidence for a conformational change in the alpha subunit during catalysis.

Acetyl coenzyme A synthase (ACS) is an alpha2beta2 tetramer in which the active-site A-cluster, located in the alpha subunits, consists of an Fe4S4 cubane bridged to a {Nip Nid} binuclear site. The alpha subunits exist in two conformations. In the open conformation, Nip is surface-exposed, while the proximal metal is buried in the closed conformation.

Evidence for a proton transfer network and a required persulfide-bond-forming cysteine residue in Ni-containing carbon monoxide dehydrogenases.

Carbon monoxide dehydrogenase from Moorella thermoacetica catalyzes the reversible oxidation of CO to CO(2) at a nickel-iron-sulfur active site called the C-cluster. Mutants of a proposed proton transfer pathway and of a cysteine residue recently found to form a persulfide bond with the C-cluster were characterized. Four semiconserved histidine residues were individually mutated to alanine.

Inactivation of acetyl-CoA synthase/carbon monoxide dehydrogenase by copper.

Two recent crystal structures of acetyl-CoA synthase (ACS) from Moorella thermoacetica exhibited different metal contents and geometries at their active site, called the A-cluster. This led to the proposal of two catalytic mechanisms, one Ni-based, the other Cu-based. ACS was studied with respect to synthase activity, methyl group transfer activity, metal content, and EPR spectroscopy.