ISOLATION, CHARACTERIZATION, AND FUNCTIONAL-ROLE OF THE HIGH-POTENTIAL IRON-SULFUR PROTEIN (HIPIP) FROM RHODOFERAX FERMENTANS

A new high-potential iron-sulfur protein (HiPIP) has been isolated and purified to homogeneity from the soluble fraction obtained from light -grown cells of the facultative photoheterotrophic bacterium Rhodofera x fermentans. The new protein was identified as a HiPIP by virtue of i ts molecular properties such as the molecular mass (M(r) = 8.7 kDa), t he Fe/protein ratio (3.8 +/- 0.2), the reduction potential (E(m,7) = 351 mV), the electronic spectrum of the reduced and the oxidized prote in, and the EPR spectrum of the oxidized protein, These molecular prop erties lie in the range observed for HiPIPs from other sources and, in particular, the iron content is consistent with the presence of one [ Fe4S4] cubane cluster per molecule, The isoelectric pH values of the t wo redox forms are consistent with a basic protein, Kinetic studies of HiPIP oxidation, performed by monitoring the absorbance changes induc ed upon light excitation of the photosynthetic reaction center, give d irect evidence of the role of the HiPIP in the photosynthetic electron transfer chain of Rf. fermentans. (C) 1995 Academic Press, Inc.