Isolation of the Photoactive Reaction Center Complex that Contains Three Types of Fe-S Centers and a CytochromecSubunit from the Green Sulfur BacteriumChlorobium limicolaf.thiosulfatophilum, Strain Larsen

摘要

The photoactive reaction center (RC) complex from the green sulfur bacteriumChlorobium limicola f.thiosulfatophilum, strain Larsen, was isolated after solubilization and ammonium sulfate fractionation followed by ion-exchange chromatography. The spectrum of the complex was almost identical with that of the similar RC complex isolated by Feiler et al. [(1992)Biochemistry31: 2608–2614] except for the presence of cytochromec551instead ofc553in the latter study. A molecular ratio of BChlato P840 of the isolated RC complex was assayed to be 25–35. SDSPAGE analysis revealed that the isolated complex contained three major polypeptides with apparent molecular masses of 68, 41 and 21 kDa, respectively. The 21-kDa polypeptide was identified to be a heme-binding protein by staining the gel for peroxidase activity. The cytochromec551was oxidized by flash light in a biphasic manner with half times of 90 and 390μs, respectively, that coincided with the reduction half times of P840+. Three distinct iron-sulfur centers assigned to FA, FBand Fx, respectively, from their g-values were detected by EPR spectroscopy at cryogenic temperature. These results suggest that the present preparation contains a minimal functional unit of the RC of this bacterium, and that this complex appears to lie on a evolutionary line between RC's of purple bacteria and photosyst