Isolation and characterization of the membrane-bound cytochrome c-554 from the thermophilic green photosynthetic bacterium Chloroflexus aurantiacus |
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Authors: | John C Freeman Robert E Blankenship |
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Institution: | (1) Department of Chemistry, Arizona State University, 85287-1604 Tempe, AZ, USA;(2) Center for Study of Early Events in Photosynthesis, 85287-1604 Tempe, AZ, USA;(3) Present address: Department of Chemistry, The Pennsylvania State University, 16802 University Park, PA, USA |
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Abstract: | The membrane-bound photooxidizable cytochrome c-554 from Chloroflexus aurantiacus has been purified. The purified protein runs as a single heme staining band on SDS-PAGE with an apparent molecular mass of 43 000 daltons. An extinction coefficient of 28 ± 1 mM–1 cm–1 per heme at 554 nm was found for the dithionite-reduced protein. The potentiometric titration of the hemes takes place over an extended range, showing clearly that the protein does not contain a single heme in a well-defined site. The titration can be fit to a Nernst curve with midpoint potentials at 0, +120, +220 and +300 mV vs the standard hydrogen electrode. Pyridine hemochrome analysis combined with a Lowry protein assay and the SDS-PAGE molecular weight indicates that there are a minimum of three, and probably four hemes per peptide. Amino acid analysis shows 5 histidine residues and 29% hydrophobic residues in the protein. This cytochrome appears to be functionally similar to the bound cytochrome from Rhodopseudomonas viridis. Both cytochrome c-554 from C. aurantiacus and the four-heme cytochrome c-558-553 from R. viridis appear to act as direct electron donors to the special bacteriochlorophyll pair of the photosynthetic reaction center. They have a similar content of hydrophobic amino acids, but differ in isoelectric point, thermodynamic characteristics, spectral properties, and in their ability to be photooxidized at low temperature.Abbreviations LDAO
lauryl dimethyl amine-N-oxide
- SDS-PAGE
sodium dodecyl sulfate polyacrylamide gel electrophoresis
- mV
millivolt
- Em.8
midpoint potential at pH 8.0
- ODV
optical density x volume in ml |
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Keywords: | cytochrome c photosynthesis photosynthetic bacteria electron transport Chloroflexus aurantiacus green bacteria |
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