Reconstitution of electron transport by cytochrome c-553 in a cell-free system of Nostoc muscorum

Abstract

Treatment of spheroplasts of Nostoc museorum with hypotonic buffer results in membranes depleted of cytochrome c-553, but still active in photosynthetic and respiratory electron transport. These membranes retain full photosystem II activity (H2O→DADox). Complete linear electron transport (H2O→NADP(+)), however, is decreased as compared with untreated spheroplasts. Addition of basic Nostoc cytochrome c-553 to depleted membranes reconstitutes NADP(+) reduction and redox reactions of the photosystem I region as well.Using NADPH as electron donor, respiration of depleted membranes is also stimulated by adding cytochrome c-553, indicative of its function in respiratory electron transport.Cytochrome c-553 from Bumilleriopsis filiformis, Spirulina platensis (acidic types), Phormidium foveolarum (basic type), and mitochondrial horse-heart cytochrome c-550 are not effective in reconstituting both photosynthetic and respiratory electron transport, which points to a specific role of Nostoc cytochrome c-553.

Interaction of photosynthesis, respiration and nitrogen fixation in cyanobacteria

“…Therefore, the dual role of cytochrome c and/or plastocyanin cannot safely be deduced from such type of experiments. Using a membrane preparation from Nostoc muscorum, Stiirzl et al (1982) could restore electron flow from water to NADP in the light and from NAD(P)H to oxygen in the dark by adding Nostoc cytochrome c-553, which, accordingly, not only donated electrons to the oxidase and P-700 but also accepted eleetron/s from the cytochrome b6/f complex. Only the Nostoc cytochrome was active in this membrane preparation, not even cytochromes isolated from other cyanobacteria were found active.…”

Terminal oxidases of cyanobacteria

“…Most of the initial studies were carried out with horse heart cytochrome c; cyanobacterial COX generally shows high reactivity towards this protein [14]. In terms of physiological donors, Pc and Cyt c 6 , the electron donors to Photosystem I in cyanobacterial photosynthesis, are capable of interacting with COX [3,[15][16][17]. This has been reviewed by Peschek et al [8,11].…”

Cyanobacterial Respiration

“…Respiratory electron transport (from NADPH to in the same membranes, however, could be reconstituted with any of the cytochromes c tested, including the one from N. muscorum . Stürzl et al (1982) also measured the residual amount of cytochrome present in their membrane preparations and showed it to depend on the isolation procedure. Light-driven electron transport from either or NADH to NADPH (via ferredoxin and FNR) in membranes from Anabaena variabilis heterocysts could be restored by the addition of cytochrome or plastocyanin .…”