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The green photosynthetic bacterium Chloroflexus aurantiacus, which belongs to the phylum of filamentous anoxygenic phototrophs, does not contain a cytochrome bc or bf type complex as is found in all other known groups of phototrophs. This suggests that a functional replacement exists to link the reaction center photochemistry to cyclic electron transfer as well as respiration. Earlier work identified a potential substitute of the cytochrome bc complex, now named alternative complex III (ACIII), which has been purified, identified and characterized from C. aurantiacus. ACIII functions as a menaquinol:auracyanin oxidoreductase in the photosynthetic electron transfer chain, and a related but distinct complex functions in respiratory electron flow to a terminal oxidase. In this work, we focus on elucidating the structure of the photosynthetic ACIII. We found that AC III is an integral-membrane protein complex of around 300 kDa that consists of 8 subunits of 7 different types. Among them, there are 4 metalloprotein subunits, including a 113 kDa ironsulfur cluster-containing polypeptide, a 25 kDa penta-heme c-containing subunit and two 20 kDa mono-heme c-containing subunits in the form of a homodimer. A variety of analytical techniques were employed in determining the ACIII substructure, including HPLC combined with ESI-MS, metal analysis, potentiometric titration and intensity analysis of heme-staining SDS-PAGE. A preliminary structural model of the ACIII complex is proposed based on the analytical data and chemical cross-linking in tandem with mass analysis using MALDI-TOF, as well as transmembrane and transit peptide analysis.Bacterial electron transport pathways largely fall into two major categories: the light-driven photosynthetic electron transfer chain and the aerobic or anaerobic respiratory electron transfer chain. Despite the vast differences between photo-and oxidative phosphorylations, they both couple the chemical reactions between electron donors and electron accepters to the translocation of protons across the membrane, which then drives ATP formation and other energy-dependent processes (1). As a result, the common feature of all electron transport chains is the presence of a proton pump to create the transmembrane proton gradient. In respiratory electron transfer pathways, there may be as many as three types of proton pumping protein complexes reminiscent of mitochondria, depending on * Address correspondence to: Robert E. Blankenship, Washington University in St. Louis, One Brookings Dr., CB 1137, St. Louis, . blankenship@wustl.edu. Supporting information available The identification of the cross-linked products. This supplementary material is available free of charge via the internet at http://pubs.acs.org. NIH Public Access Author ManuscriptBiochemistry. Author manuscript; available in PMC 2011 August 10. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript environmental factors (2). In contrast, the proton pump in all the photosynthetic electron transfer chains was u...

GeoExposures is a newly developed crowd-sourcing web site for recording temporary geological exposures in the Great Britain that might be lost to science. It has been developed and deployed by the British Geological Survey (BGS) using the Ushahidi Crowdmap service. Geological site information can be recorded and uploaded using a 'smart phone' or via a personal computer to the common-access web site. Geological data is recorded using a pro-forma and is uploaded along with digital photographs. Support is provided through linked web sites including Google Maps, BGS digital geological maps, the BGS Stratigraphical Lexicon and BGS TimeChart (geochronology). As a contribution to citizen science, GeoExposures will enable the geoscience community to contribute to preserving important geological information. Geoexposures is made available under a Creative Commons licence. As with other citizen-science initiatives, the information and photographic records are available to the community and copyright is not vested with the individual respondent or BGS.

No abstract

Cytochrome c6, (cyt c6) a soluble monoheme electron transport protein, was isolated and characterized from the chlorophyll d-containing cyanobacterium Acaryochoris marina, the type strain MBIC11017. The protein was purified using ammonium sulfate precipitation, ion exchange and gel filtration column chromatography, and fast performance liquid chromatography. Its molecular mass and pI have been determined to be 8.87 kDa and less than 4.2, respectively, by mass spectrometry and isoelectrofocusing (IEF). The protein has an alpha helical structure as indicated by CD (circular dichroism) spectroscopy and a reduction midpoint potential (Em) of +327 mV versus the normal hydrogen electrode (NHE) as determined by redox potentiometry. Its potential role in electron transfer processes is discussed.