Effect of O2 Concentration on Dark H2 Oxidation in Whole Cells of a Marine Sulfur Photosynthetic Bacterium (Chromatium sp. Strain Miami PBS 1071)

Whole cells of photoanaerobically grown Chromatium sp. strainMiami PBS 1071, a marine purple sulfur bacterium, oxidized H₂in the dark through the oxyhydrogen reaction. Oxidation of H₂was measured by injecting either H₂ into an air-equilibratedcell suspension (microaerobic H₂ oxidation) or O₂ into an H₂/Ar-equilibratedcell suspension (microaerobic H₂ oxidation). Both types of H₂oxidation were strongly inhibited by azide (40 mM), indicatingthat the oxidation proceeds via a terminal oxidase system. 2,5-Dibromo-3-methyl-6-isopropyl-p-benzoquinone(16 µM) inhibited aerobic H₂ oxidation by 49% but it acceleratedmicroacrobic H₂ oxidation. The sensitivity of H₂ oxidation torotenone was higher under aerobic conditions. The results indicatethat H₂ oxidation proceeds via two different pathways; one containsubiquinone and NAD, and the other does not. The contributionof each pathway depends on the O₂ partial pressure. ⁴ Present address: Institute of Oceanic Research and Development,Tokai University, Shimizu, Shizuoka 424, Japan. (Received May 24, 1985; Accepted August 29, 1985)     

A far-red absorbing form of chlorophyll formed by the action of aminotriazole

A far-red absorbing pigment with an absorption maximum at 742nm was formed in wheat leaves treated with amitrol. Spectralchanges of this pigment on treatment with Triton X-100 or acetonesuggested that the pigment is a form of chlorophyll producedby inhibition of a step of chlorophyll biosynthesis during chloroplastdevelopment. (Received November 16, 1971; )     

Effects of cationic and anionic chain compounds on absorption spectra and photochemical activities of chloroplasts

The effects of ionic chain compounds on absorption spectra andphotochemical activities of spinach chloroplasts in suspensionwere investigated and compared with the effects of non-ionicchain compounds previously studied. Two types of spectral changestook place when chloroplasts were treated with ionic compounds.One type of change, not observable with non-ionic chain compoundssuch as carotenoids and fatty alcohols, was in the efficiencyof light absorption; absorption bands over the whole visibleregion were either intensified or flattened at low reagent concentrations.Intensification was observed with anionic fatty acids with 10–18carbon atoms and ascribed to swelling of whole chloroplasts,while flattening was observed with cationic primary and quarternaryamines and ascribed to aggregation of chloroplasts. The othertype of spectral change, transformation of bands observed athigh concentrations of ionic chain compounds, was essentiallysimilar to that found with non-ionic chain compounds. The redand Soret bands of chlorophylls were transformed and absorptionin the range of 490–520 nm decreased on treatment withionic chain compounds. Activity of photosystem I was enhancedby reagents at low concentrations and inhibited at high concentrations,while activity of photosystem II decreased in a middle concentrationrange. These activity changes were correlated to the spectralchanges, although the correlations were less marked than thosefound with non-ionic compounds. This is probably because ofoverlapping of the two types of changes which occur with ionicchain compounds. (Received March 8, 1972; )     

Heterologous expression of the gene for the ethylene-forming enzyme fromPseudomonas syringae in the cyanobacteriumSynechococcus

Summary Bioconversion of atmospheric carbon dioxide to ethylene was studied in a recombinant cyanobacterium. The gene for the ethylene-forming enzyme ofPseudomonas syringae pv.phaseolicola PK2 was cloned and expressed in the cyanobacteriumSynechococcus PCC7942 R2-SPc by use of a shuttle vector pUC303. The ethylene-forming activityin vivo ofSynechococcus PCC7942 R2-SPc that carried the gene for the ethylene-forming enzyme ofP. syringae pv.phaseolicola PK2 was one-fifth of that ofE. coli JM109 that harbored the same plasmid. The enzyme accounted for 0.021% by weight of the total soluble protein inSynechococcus PCC7942 R2-SPc.     

The role of light in formation of modified S2-state upon low pH-treatment of oxygen-evolving Photosystem II

An abnormal, structurally modified, kinetically stable S₂-state has been reported to be induced when Photosystem II was treated with NaCl-EGTA (or EDTA) in the light or with pH in darkness, both are assumed to release functional Ca²⁺. In order to compare the mechanism of induction of modified S₂-state between the two treatments, effects of illumination during or before low pH-treatment on formation of the abnormal S₂-state were investigated by means of thermoluminescence measurements and low temperature EPR spectroscopy. Following results have been obtained: Flash illumination during low pH-treatment did not practically induce the abnormal S₂-state, whereas preflash illumination given immediately before low pH-treatment efficiently induced the abnormal S₂-state, and its amplitude showed a period-four oscillation on varying the preflash number with maxima at the second and sixth flashes. The abnormal S₂-state thus induced by preflashes was identical with the modified S₂-state that could be induced in dark-low pH-treated Photosystem II by excitation at 0°C after neutralization to pH 6.5. It was inferred that in low pH-treatment, modified S₂-state can be formed from both S₂- and S₃-states, but its yield from the latter is much higher than from the former, consistent with the early results by Boussac et al. obtained for NaCl-EGTA-light or NaCl-citrate-light treatment.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EDTA ethylenediaminetetraactate - EGTA ethylene glycol bis(-aminoethylether)-N,N,N,N-tetraacetic acid - Mes 2-(N-morpholino)ethanesulfonic acid - PS II Photosystem II     

A Novel 3.5 kDa Protein Component of Cyanobacterial Photosystem I Complexes

A novel protein component of 3.5 kDa was detected in photosystemI complexes prepared from several cyanobacteria, viz. Synechococcusvulcanus, Synechococcus elongotus BP-1, Synechococcus sp. FCC7002 and Synechocystis sp. FCC 6803. The complete amino acidsequence of this component was determined by direct proteinsequencing. The sequences of the 3.5 kDa proteins from thesefour organisms were highly homologous to each other, featuringa hydrophobic domain in the middle. The cyanobacterial consensussequence exhibits significant homology to the presumed productof ORF32 in the chloroplast DNA of liverwort (Marchantia polymorpha),but no homologous ORF is present in the chloroplast DNA of tobaccoor rice. Since this protein appears to interact strongly withthe PS I reaction center complex, it may play some role in thefunction and maintenance of the structure of PS I. (Received May 25, 1992; Accepted August 18, 1992)     

Structural insights into the Thermus thermophilus ADP-ribose pyrophosphatase mechanism via crystal structures with the bound substrate and metal

ADP-ribose pyrophosphatase (ADPRase) catalyzes the divalent metal ion-dependent hydrolysis of ADP-ribose to ribose 5'-phosphate and AMP. This enzyme plays a key role in regulating the intracellular ADP-ribose levels, and prevents nonenzymatic ADP-ribosylation. To elucidate the pyrophosphatase hydrolysis mechanism employed by this enzyme, structural changes occurring on binding of substrate, metal and product were investigated using crystal structures of ADPRase from an extreme thermophile, Thermus thermophilus HB8. Seven structures were determined, including that of the free enzyme, the Zn(2+)-bound enzyme, the binary complex with ADP-ribose, the ternary complexes with ADP-ribose and Zn(2+) or Gd(3+), and the product complexes with AMP and Mg(2+) or with ribose 5'-phosphate and Zn(2+). The structural and functional studies suggested that the ADP-ribose hydrolysis pathway consists of four reaction states: bound with metal (I), metal and substrate (II), metal and substrate in the transition state (III), and products (IV). In reaction state II, Glu-82 and Glu-70 abstract a proton from a water molecule. This water molecule is situated at an ideal position to carry out nucleophilic attack on the adenosyl phosphate, as it is 3.6 A away from the target phosphorus and almost in line with the scissile bond.     

Molecular characterization and gene expression of lhcb5 gene encoding CP26 in the light-harvesting complex II of Chlamydomonas reinhardtii

We isolated and sequenced a cDNA clone encoding a minor chlorophyll a/b-binding protein, CP26, which is associated with the light-harvesting complex II of Chlamydomonas reinhardtii. Protein sequences of internal peptide fragments from purified CP26 were determined and used to identify a cDNA clone. The 1.1 kb lhcb5 gene codes for a polypeptide of 289 amino acids with a predicted molecular weight of 30713. The lhcb5 gene product could reconstitute with chlorophylls and xanthophylls to form a green band on a gel. Although the expression of many lhcb genes are strictly regulated by light, the lhcb5 gene was only loosely regulated. We propose that a plant acclimatizes itself to the light environment by quantitatively and qualitatively modulating the light-harvesting complex. Characterization of the primary structure and the implications of its unique expression are discussed.     

Inhibitory effect of p-nitrothiophenol in the light on the Photosystem II activity of spinach chloroplasts

The treatment of spinach chloroplasts with p-nitrothiophenol in the light at acidic and neutral pH's caused specific inhibition of the Photosystem II activity, whereas the same treatment in the dark did not affect the activity at all. The photosystem I activity was not inhibited by p-nitrothiophenol both in the light and in the dark. The inhibition was accompanied by changes of fluorescence from chloroplasts. As observed at room temperature, the 685-nm band was lowered by the p-nitrothiophenol treatment in the light and, at liquid nitrogen temperature, the relative height of the 695-nm band to the 685-nm band increased and the 695-nm band shifted to longer wavelengths. The action spectra for these effects of p-nitrothiophenol on the activity and fluorescence showed a peak at 670 nm with a red drop at longer wavelengths. It was concluded that the light absorbed by Photosystem II is responsible for the chemical modification of chloroplasts with p-nitrothiophenol to causing the specific inhibition of Photosystem II.     

泥河湾盆地几处旧石器时代文化遗址光释光测年

中国泥河湾盆地几处旧石器时代考古遗址经过光释光年代测试,分别得出IRSL和BLSL年龄。油房遗址文化层上下部层位分别为1.3—1.4万年和1.5—1.7万年,虎头梁遗址上部层位为0.9±0.13万年,许家窑遗址文化层约为6.9±0.8万年。