Immunological and spectral characterization of partly purified cytochrome oxidase from the cyanobacterium Synechocystis 6714

The bioenergetic role of dioxygen and the terminal oxidase(s) in cyanobacteria

Owing to the release of 13 largely or totally sequenced cyanobacterial genomes (see and ), it is now possible to critically assess and compare the most neglected aspect of cyanobacterial physiology, i.e., cyanobacterial respiration, also on the grounds of pure molecular biology (gene sequences). While there is little doubt that cyanobacteria (blue-green algae) do form the largest, most diversified and in both evolutionary and ecological respects most significant group of (micro)organisms on our earth, and that what renders our blue planet earth to what it is, viz. the O(2)-containing atmosphere, dates back to the oxygenic photosynthetic activity of primordial cyanobacteria about 3.2x10(9) years ago, there is still an amazing lack of knowledge on the second half of bioenergetic oxygen metabolism in cyanobacteria, on (aerobic) respiration. Thus, the purpose of this review is threefold: (1) to point out the unprecedented role of the cyanobacteria for maintaining the delicate steady state of our terrestrial biosphere and atmosphere through a major contribution to the poising of oxygenic photosynthesis against aerobic respiration ("the global biological oxygen cycle"); (2) to briefly highlight the membrane-bound electron-transport assemblies of respiration and photosynthesis in the unique two-membrane system of cyanobacteria (comprising cytoplasmic membrane and intracytoplasmic or thylakoid membranes, without obvious anastomoses between them); and (3) to critically compare the (deduced) amino acid sequences of the multitude of hypothetical terminal oxidases in the nine fully sequenced cyanobacterial species plus four additional species where at least the terminal oxidases were sequenced. These will then be compared with sequences of other proton-pumping haem-copper oxidases, with special emphasis on possible mechanisms of electron and proton transfer.

Soluble CuA Domain of Cyanobacterial Cytochrome c Oxidase

The genomes of several cyanobacteria show the existence of gene clusters encoding subunits I, II, and III of aa(3)-type cytochrome c oxidase. The enzyme occurs on both plasma and thylakoid membranes of these oxygenic phototrophic prokaryotes. Here we report the expression and purification of a truncated subunit II copper A (Cu(A)) domain (i.e. the electron entry and donor binding site) of cytochrome c oxidase from the cyanobacterium Synechocystis PCC 6803 in high yield. The water-soluble purple redox-active bimetallic center displays a relatively low standard reduction potential of 216 mV. Its absorption spectrum at pH 7 is similar to that of other soluble fragments from aa(3)-type oxidases, but the insensitivity of both absorbance and circular dichroism spectra to pH suggests that it is less exposed to the aqueous milieu compared with other Cu(A) domains. Oxidation of horse heart cytochrome c by the bimetallic center follows monophasic kinetics. At pH 7 and low ionic strength the bimolecular rate constant is (2.1 +/- 0.3) x 10(4) m-1 s(-1), and the rates decrease upon the increase of ionic strength. Sequence alignment and modeling of cyanobacterial Cu(A) domains show several peculiarities such as: (i) a large insertion located between the second transmembrane region and the putative hydrophobic cytochrome c docking site, (ii) the lack of acidic residues shown to be important in the interaction between cytochrome c and Paracoccus Cu(A) domain, and (iii) an extended C terminus similar to Escherichia coli ubiquinol oxidase.

The respiratory chain of blue-green algae (cyanobacteria)

Electron transport components on the way from reduced substrates to the terminal respiratory oxidase(s) are discussed in relation to analogous and/or homologous enzymes and electron carriers in the generally much better known bacteria, mitochondria and chloroplasts. The kinetic behaviour of the components, their localization within the cell and their evolutionary position are given special attention. Pertinent results from molecular genetics are also mentioned. The unprecedented role of cyanobacteria for our biosphere and our whole planet earth appears to deserve a more extended introductory chapter.

Rapid purification of cytochrome c oxidase from Paracoccus denitrificans

Two methods are described for the purification of cytochrome c oxidase from Triton X-100 extracts of the periplasma membrane of Paracoccus denitrificans. The first is a large-scale procedure for the preparation of 100-250 nmol of cytochrome c oxidase (10-20 mg) in 1 week. The second is a rapid procedure for isolating up to 25 nmol in 2-3 days. Owing to the high yields given by fast protein liquid chromatography (FPLC) on Mono Q columns, the overall yield is about 20%, whereas the yield in many other previously published procedures does not exceed 10%. The use of FPLC on Mono Q also offers a considerable saving of time.

Changes of some physical properties of isolated and purified plasma and thylakoid membrane vesicles from the freshwater cyanobacterium Synechococcus 6301 (Anacystis nidulans) during adaptation to salinity

Photoautotrophically growing cultures of the freshwater cyanobacterium Anacystis nidulans (Synechococcus sp.) became adapted to the presence of 0.4-0.5 M NaCl in the growth medium (about seawater level) with a lag phase of 2 days after which time the growth rate resumed at 80-90% of the control. Major changes in structure and function of the plasma membranes (and, to a much lesser extent, of the thylakoid membranes) were found to accompany the adaptation process. Plasma and thylakoid membranes were separated from crude cell-free extracts of French pressure cell-treated Anacystis by discontinuous sucrose density gradient centrifugation and purified by repeated recentrifugation on fresh gradients. Concentrations of copper, iron, calcium, and magnesium ions were determined by inductively coupled plasma atomic emission spectrometry with EDTA-washed and dialyzed membrane preparations; salt adaptation was found to increase (decrease) the concentration of membrane-bound calcium in plasma (thylakoid) membranes, qualitatively reciprocal results being obtained for magnesium. Levels of plasma membrane-bound copper and iron roughly tripled during the adaptation process; by contrast, corresponding effects on thylakoid membranes were negligible. The size of the membrane vesicles was measured by quasi-elastic laser light-scattering and the electric surface charge of the membranes was measured by laser Doppler velocimetry. Salt adaptation decreased the mean diameter of plasma membrane vesicles to a much higher extent than that of thylakoid membrane vesicles. Overall surface charge densities of resting vesicles were only slightly affected by the salt treatment as was also seen from titration of the electrophoretic mobility of the vesicles with electrolytes. Yet, induction of (photosynthetic or respiratory) electron transport provoked a charge separation across the membrane which was easily measurable in terms of electrophoretic mobility. The results will be discussed with particular emphasis on the stimulated cytochrome c oxidase activity of plasma (but not thylakoid) membranes from salt-adapted cells compared to control cells and also with respect to the decreased ion permeability of the plasma membrane of salt grown cells.

Detection of chlorophyllide in chlorophyll-free plasma membrane preparations from Anacystis nidulans

Plasma and thylakoid membranes were isolated and purified from the cyanobacterium Anacystis nidulans. Spectrophotometric examination of acetone extracts gave major absorption bands resulting from carotenoids and chlorophyll a in plasma and thylakoid membranes, respectively. Only a very small absorption peak at 663 nm was detected in acetone extracts of plasma membranes which, in contrast to the corresponding peak from thylakoid membranes, could not be extracted into n-hexane; methanol, on the other hand, was effective with both plasma and thylakoid membranes. Aqueous membrane suspensions excited at 435 nm gave strong fluorescence emission at 662 nm for plasma membranes, but only a very small one for thylakoid membranes which had been adjusted to equal absorbance at 678 nm. Excitation spectra of the 668 nm fluorescence emission peak in acetone extracts of plasma and thylakoid membranes were strikingly different from each other. Finally, high performance liquid chromatography afforded clear-cut preparative separation of the two "chlorophyll-like" pigments in plasma and thylakoid membranes, respectively, and identification by comparison with retention characteristics known from the literature, together with a pure chlorophyll a standard. Our results indicate that the highly fluorescent and polar "chlorophyll-like" pigment in plasma membranes of Anacystis is a chlorophyll precursor, viz. chlorophyllide a.