No abstract

Photosynthetic and respiratory electron-transport reactions by the blue-green alga, Anabaena variabilis, exhibit a strict temperature dependence in vivo as well as in the cell-free system. The ratio of respiratory oxygen uptake in the dark and oxygen evolution in the light is high after growth at low temperatures (20 °C) and low after growth under optimum temperatures (28 °C). Respiration and photosynthesis show different break temperatures in the Arrhenius plots. Increase of growth temperature yields higher break points for photosynthetic or respiratory electron transport as well. These data are taken as evidence that photosynthetic and respiratory electron transport chains are embedded in different membrane areas.

An antibody prepared against purified cytochrome c-553 from Nostoc muscorum inhibits the redox function of cytochrome c-553 as checked by a diaphorase assay. 20 to 30% inhibition of NADPH-driven respiratory and light-induced oxygen uptake by Nostoc thylakoids is observed when cytochrome c-553 specific antibodies were applied. However, only 30 to 50% of the total cytochrome c-553 content is released from isolated membrane material, thus being accessible to antibodies. Supplementing the isolated membrane material with excess Nostoc cytochrome before adding the antibody abolishes inhibition. The data provide further evidence for soluble cytochrome c-553 being a link between photosynthetic and respiratory electron transport in blue- green algae.

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.

Membranes isolated from vegetative cells of Anabaena variabilis (ATCC 29413) oxidine NADPH and NADH in a cyanide‐sensitive reaction, NADPH being the better donor. In addition, both act as reductants for photosystem I in the light and in the presence of DCMU. An NADH‐regenerating system has been introduced experimentally, functioning as donor system for photosystem I of Anabaena membranes. This NADH dehydrogenation is strictly light‐dependent, sensitive to DBMIB, establishes a transhydrogenase system with NADP+ was hydrogen acceptor and competes with oxygen. Kinetic analysis of oxygen uptake with reference to nucleotide concentration exhibited different Km‐ and Vmax‐values for NADPH and NADH in the light and in the dark.