Purification of cytochrome b-561 from bean hypocotyls plasma membrane.: Evidence for the presence of two heme centers

The high potential, ascorbate-reducible b-type cytochrome of plant plasma membranes, named cytochrome b-561, has been purified to homogeneity from etiolated bean hypocotyls. The pure protein migrated in denaturing electrophoresis as a broad band of approximately 55 kDa, and was found to be glycosylated. Optical redox titrations of partially purified cytochrome b-561 indicated that it contains two hemes with similar spectral features, but distinct midpoint redox potentials (E-m7+135 mV and +206 mV, respectively). The presence of two heme centers in cytochrome b-561 is consistent with its role in electron transfer across plant plasma membranes. (C) 2000 Elsevier Science B.V. All rights reserved.