Isolation and Properties of Two Soluble Heme Proteins in Extracts of the Photoanaerobe Chromatium

Abstract

The involvement of heme proteins in photometabolism, first suggested by Hill (1, 2), seems certain from results of recent enzyme studies (3-5) and observations on systems in viva using differential spectrophotometry (6-10). Of the many heme proteins which exist in intimate association with the photoactive pigments in the functional subcellular structures of photosynthetic tissues, only three have been isolated in soluble form in sufficient amounts and purity for adequate characterization. One of these is the so-called “cytochrome f” of green plant tissues (11). The other two are variant cytochromes, one of the V type (12), and one an atypical heme protein called “RHP” (12, 13) obtained from extracts of the facultative photoheterotrophic purple bacterium, Rhodospirillum rubrum. We now report the isolation and identification of two soluble heme proteins contained in extracts of the obligate photoanaerobit purple bacterium, Chromatium. Previous studies (14, 15) have indicated the existence of both a cytochrome ‘Y-type and an RHP-type heme protein’ in partially resolved preparations (15). Some preliminary data have been published on their physicochemical properties. Complete resolution of these heme protein mixtures has been achieved so that it is now possible to characterize completely the two soluble Chromutium cytochrome components.