On the mechanism of photosynthetic electron transfer in Rhodopseudomonas capsulata and Rhodopseudomonas sphaeroides

(1) Current models for the mechanism of cyclic electron transport in Rhodopseudomonas sphaeroides and Rhodopseudomonas capsulata have been investigated by observing the kinetics of electron transport in the presence of inhibitors, or in photosynthetically incompetent mutant strains. (2) In addition to its well-characterized effect on the Rieske-type iron sulfur center, 5-(n-undecyl)-6-hydroxy-4,7-dioxobenzothiazole (UHDBT) inhibits both cytochrome b₅₀ and cytochrome b_?90 reduction induced by flash excitation in Rps. sphaeroides and Rps. capsulata. The concentration dependency of the inhibition in the presence of antimycin (approx. 2.7 mol UHDBT/mol reaction center for 50% inhibition of extent) is very similar to that of its inhibition of the antimycin-insensitive phase of ferricytochrome c re-reduction. UHDBT did not inhibit electron transfer between the reduced primary acceptor ubiquinone (Q^?_I) and the secondary acceptor ubiquinone (Q_II) of the reaction center acceptor complex. A mutant of Rps. capsulata, strain R126, lacked both the UHDBT and antimycin-sensitive phases of cytochrome c re-reduction, and ferricytochrome b₅₀ reduction on flash excitation. (3) In the presence of antimycin, the initial rate of cytochrome b₅₀ reduction increased about 10-fold as the E_h(7.0) was lowered below 180 mV. A plot of the rate at the fastest point in each trace against redox potential resembles the Nernst plot for a two-electron carrier with E_m(7.0) ≈ 125 ± 15 mV. Following flash excitation there was a lag of 100–500 μs before cytochrome b₅₀ reduction began. However, there was a considerably longer lag before significant reduction of cytochrome c by the antimycin-sensitive pathway occurred. (4) The herbicide ametryne inhibited electron transfer between Q^?_I and Q_II. It was an effective inhibitor of cytochrome b₅₀ photoreduction at E_h(7.0) 390 mV, but not at E_h(7.0) 100 mV. At the latter E_h, low concentrations of ametryne inhibited turnover after one flash in only half of the photochemical reaction centers. By analogy with the response to o-phenanthroline, it is suggested that ametryne is ineffective at inhibiting electron transfer from Q^?_I to the secondary acceptor ubiquinone when the latter is reduced to the semiquinone form before excitation. (5) At E_h(7.0) > 200 mV, antimycin had a marked effect on the cytochrome b₅₀ reduction-oxidation kinetics but not on the cytochrome c and reaction center changes or the slow phase III of the electrochromic carotenoid change on a 10-ms time scale. This observation appears to rule out a mechanism in which cytochrome b₅₀ oxidation is obligatorily and kinetically linked to the antimycin-sensitive phase of cytochrome c reduction in a reaction involving transmembrane charge transfer at high E_h values. However, at lower redox potentials, cytochrome b₅₀ oxidation is more rapid, and may be linked to the antimycin-sensitive reduction of cytochrome c. (6) It is concluded that neither a simple linear scheme nor a simple Q-cycle model can account adequately for all the observations. Future models will have to take account of a possible heterogeneity of redox chains resulting from the two-electron gate at the level of the secondary quinone, and of the involvement of cytochrome b_?90 in the rapid reactions of the cyclic electron transfer chain     

Differential extraction of sediment phosphates with NTA solutions

An extraction technique is described for the separation of iron- and calcium-bound phosphate. The iron-bound phosphate is extracted with a 0.05 M solution of Ca-NTA under reducing conditions. Iron, also, is brought into solution, which is an advantage over the NaOH extraction. The calcium-bound phosphate is extracted with a 0.05 M solution of Na-NTA. The NTA also extracts humic compounds. Organic phosphate compounds can be measured in the NTA extracts, unlike the NaOH or H₂SO₄ extracts such as are used in the (modified) Jackson procedure.Examples of some test compound extractions and of a calcareous sediment are given.     

The fractionation of iron-phosphorus compounds in sediments studied by Mössbauer spectroscopy

Iron compounds of phosphorus form a large part of the phosphorus bound in sediments. Mössbauer spectroscopy is a technique that enables us to study, directly, chemical forms of iron in solid samples. Mössbauer spectroscopy allowed us to check, directly, the selectivity of the extraction scheme for soil phosphorus proposed by Chang &; Jackson (1957), but only as far as the iron compounds are concerned. It appears that selectivity of the extraction method leaves much to be desired.

     

Flux of reduced chemical constituents (Fe2+, Mn2+, NH inf4 sup+ and CH4) and sediment oxygen demand in Lake Erie

Sediment pore water concentrations of Fe²⁺, Mn²⁺, NH _inf4 ^sup+ and CH₄ were analyzed from both diver-collected cores and anin situ equilibration device (peeper) in Lake Erie's central basin. Sediment oxygen demand (SOD) was measured at the same station with a hemispheric chamber (including DO probe and recorder) subtending a known area of sediments. The average SOD was 9.4 mM m⁻² day⁻¹ (0.3 g m⁻² day⁻¹). From pore water gradients within the near-surface zone, the chemical flux across the interface was calculated indirectly using Fick's first law modified for sediments. These calculations, using core and peeper gradients, always showed sediment loss to overlying waters, and variations between the two techniques differed by less than an order of magnitude for Fe²⁺ and CH₄. The transport of these reduced constituents can represent a sizeable oxygen demand, ranging from less than 1% for Fe²⁺ and Mn²⁺ to as high as 26% for NH _inf4 ^sup+ , and 30% for CH₄. The average flux of these constituents could account for about a third of the SOD at the sediment-water interface of this station.     

Complexes of iron and cobalt tetrasulfonated phthalocyanines with apocytochrome c

Artificial cytochromes c have been prepared with Fe(III) and Co(III) tetrasulfonated phthalocyanines in place of heme. Their structure and properties have been investigated by difference spectroscopy, CD, epr, electrophoresis, molecular weight estimation, and potentiometric measurements. The visible absorption spectra show the main peak at 650 nm for the iron compound 685 nm for the cobalt one. It is shown by CD experiments that incorporation of Fe(III)L or Co(III)L into apocytochrome c markedly increases helical content of the protein. Its conformation is, however, significantly altered as compared with the native cytochrome c. The epr and spectroscopic data show that the iron and cobalt phthalocyanine models represent the low spin species with the metal ions in trivalent state. Electrophoresis and molecular weight estimation indicate these complexes to be monomers. Both phthalocyanine complexes have not affinity for additional ligands characteristic for hemoglobin. They react, however, with CO, NO, and CN- when they are reduced with dithionite. Moreover, Co(II)L-apocyt c is able to combine with oxygen suggesting a structural feature in common with the oxygen-carrying heme proteins. Iron(II) complex in the same conditions is oxidized directly to the ferric state. The half-reduction potentials of Fe(III)L-apocyt c and Co(III)L-apocyt c are +374 mV and +320 mV, respectively. These complexes are reduced by cytochrome c and cytochrome c reductase (cytochrome bc1).     

An ecological study of the rare rotifer species Trochosphaera solstitialis (Thorpe 1893) and the first report of the male

An ecological study of the rotifer species Trochosphaera solstitialis (Thorpe, 1893) was conducted for a period of eight months in a temporary pond in eastern Texas, U.S.A. The pond was found to be environmentally stressed and contained large amounts of decomposing vegetation. Physico-chemical factors contributing to the stressed conditions were low dissolved oxygen concentrations, low pH values, high ammonia concentrations, and high color values caused by large concentrations of iron, tannin and lignin. Large concentrations of iron, tannin, and lignin seem to be highly correlated with T. solstitialis populations. Physicochemical conditions probably eliminated predators of the rotifer, such as fish. Males of T. solstitialis were observed which never left the body cavity of the female. Males probably do not feed with an apparent rudimentary digestive system.     

The role of soluble cytochrome c-551 in cyclic electron flow-driven active transport in Chromatium vinosum

Spheroplasts have been prepared from the photosynthetic purple sulfur bacterium Chromatium vinosum by lysozyme plus ethylenediaminetetraacetic acid treatment. These spheroplasts are able to take up alanine in the light, but light-dependent alanine uptake is lost upon subsequent washing of the spheroplasts. The observations that alanine uptake driven by a potassium plus valinomycin-induced membrane potential (outside positive) is not affected by washing and that light-dependent alanine uptake can be restored by addition of the supernatant from washing suggest that a soluble electron carrier is lost during washing. Light-dependent alanine uptake in washed spheroplasts could be restored by addition of C. vinosum cytochrome c-551. Other soluble electron carriers from C. vinosum (high-potential iron protein, cytochrome ‘f’, cytochrome c′ and the flavocytochrome c-552) did not restore alanine uptake nor did a variety of other soluble electron carrier proteins from other organisms. These results suggest that cytochrome c-551 functions as an electron carrier in the cyclic electron transfer chain of C. vinosum. Mitochondrial cytochrome c (equine heart) and cytochrome c-551 from Pseudomonas aeruginosa were highly effective in restoring light-dependent alanine uptake in washed spheroplasts, making it likely that C. vinosum cytochrome c-551 is related by evolution to the same cytochrome c family as these other two c cytochromes.     

Reaction of FeBlm with DNA: Fe(II)Blm-NO.

The structure of the iron bleomycin nitric oxide complex is altered in the presence of calf thymus DNA as determined from epr studies. This altered structure predominates for one iron bleomycin nitric oxide molecule per coil of the DNA helix. In the absence of nitric oxide, as the pH is lowered, iron bleomycin dissociates in two steps, supporting the hypothesis that in-plane nitrogens may be easily perturbed.     

Congruency of phylogenies derived from different proteins

Summary This communication examines the question of phylogenetic congruency- i.e., whether or not the branching order of evolutionary trees is independent of the protein studied. It was found that trees constructed for birds on the basis of immunological comparison of their transferrins, albumins, and ovalbumins agree approximately with a published tree based on the amino acid sequences of their lysozymesc. This congruency is especially noteworthy with respect to the phylogenetic position of the chachalaca, a Mexican bird classified on morphological grounds in the family Cracidae of the order Galliformes. At the protein level, this species differs as much from non-cracid galliform birds as does the duck, which belongs to another order. Despite the organismal similarity between cracid and non-cracid galliform birds, the molecular relationship is remote. If this contrast between organismal and molecular results had been based on comparative studies with only lysozyme, one could have ascribed the contrast to the possibility that chachalaca lysozyme was paralogous, rather than orthologous, to the other bird lysozymesc. Examination of several proteins is thus desirable in cases of possible paralogy.This work was supported in part by grants GB-42028X from NSF and GM-21509 from NIH     

Observation of deuterium-labeled diacetyldeuteroporphyrin incorporated in cyanoferrimyoglobin by deuterium nuclear magnetic resonance.

Sperm whale apomyoglobin was reconstituted with selectively deuterated D₆-2,4-diacetyldeuterohemin in which the ²H label was confined to the methyl groups of the acetyl moieties. A single resonance was observed in ²H NMR of the cyanoferrimyoglobin derivative, with a chemical shift 0.80 ppm downfield of external D₁₂-TMS at pH 6.7. The corresponding chemical shift of D₆-2,4-diacetyldeuterohemin-OMe as the cyanide complex in pyridine-water was 0.96 ppm downfield of external D₁₂-TMS. The prominent HOD peak was well separated at 4.4 ppm downfield. The line width of the porphyrin ²H resonances in both the protein and free solvent environments yields evidence of considerable rotational freedom of the -CD3 groups about their axes.