D1-Asp170 is structurally coupled to the oxygen evolving complex in photosystem II as revealed by light-induced Fourier transform infrared difference spectroscopy.

We report both mid-frequency (1800-1200 cm(-)(1)) and low-frequency (670-350 cm(-)(1)) S(2)/S(1) FTIR difference spectra of photosystem II (PSII) particles isolated from wild-type and D1-D170H mutant cells of the cyanobacterium Synechocystis sp. PCC 6803. Both mid- and low-frequency S(2)/S(1) spectra of the Synechocystis wild-type PSII particles closely resemble those from spinach PSII samples, which confirms an earlier result by Noguchi and co-workers [Noguchi, T., Inoue, Y., and Tang, X.-S. (1997) Biochemistry 36, 14705-14711] and indicates that the coordination environment of the oxygen evolving complex (OEC) in Synechocystis is very similar to that in spinach. We also found that there is no appreciable difference between the mid-frequency S(2)/S(1) spectra of wild-type and of D1-D170H mutant PSII particles, from which we conclude that D1-Asp170 does not undergo a significant structural change during the S(1) to S(2) transition. This result also suggests that, if D1-Asp170 ligates Mn, it does not ligate the Mn ion that is oxidized during the S(1) to S(2) state transition. Finally, we found that a mode at 606 cm(-)(1) in the low-frequency wild-type S(2)/S(1) spectrum shifts to 612 cm(-)(1) in the D1-D170H mutant spectrum. Because this 606 cm(-)(1) mode has been previously assigned to an Mn-O-Mn cluster mode of the OEC [Chu, H.-A., Sackett, H., and Babcock, G. T. (2000) Biochemistry 39, 14371-14376], we conclude that D1-Asp170 is structurally coupled to the Mn-O-Mn cluster structure that gives rise to this band. Our results suggest that D1-Asp170 either directly ligates Mn or Ca(2+) or participates in a hydrogen bond to the Mn(4)Ca(2+) cluster. Our results demonstrate that combining FTIR difference spectroscopy with site-directed mutagenesis has the potential to provide insights into structural changes in Mn and Ca(2+) coordination environments in the different S states of the OEC.

Does histidine 332 of the D1 polypeptide ligate the manganese cluster in photosystem II? An electron spin echo envelope modulation study.

The tetranuclear manganese cluster in photosystem II is ligated by one or more histidine residues, as shown by an electron spin echo envelope modulation (ESEEM) study conducted with [(15)N]histidine-labeled photosystem II particles isolated from the cyanobacterium Synechocystis sp. strain PCC 6803 [Tang, X.-S., Diner, B. A., Larsen, B. S., Gilchrist, M. L., Jr., Lorigan, G. A., and Britt, R. D. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 704-708]. One of these residues may be His332 of the D1 polypeptide. Photosystem II particles isolated from the Synechocystis mutant D1-H332E exhibit an altered S(2) state multiline EPR signal that has more hyperfine lines and narrower splittings than the corresponding signal in wild-type PSII particles [Debus, R. J., Campbell, K. A., Peloquin, J. M., Pham, D. P., and Britt, R. D. (2000) Biochemistry 39, 470-478]. These D1-H332E PSII particles are also unable to advance beyond an altered S(2)Y(Z)(*) state, and the quantum yield for forming the S(2) state is very low, corresponding to an 8000-fold slowing of the rate of Mn oxidation by Y(Z)(*). These observations are consistent with His332 being close to the Mn cluster and modulating the redox properties of both the Mn cluster and tyrosine Y(Z). To determine if D1-His332 ligates the Mn cluster, we have conducted an ESEEM study of D1-H332E PSII particles. The histidyl nitrogen modulation observed near 5 MHz in ESEEM spectra of the S(2) state multiline EPR signal of wild-type PSII particles is substantially diminished in D1-H332E PSII particles. This result is consistent with ligation of the Mn cluster by D1-His332. However, alternate explanations are possible. These are presented and discussed.

Rapid formation of the stable tyrosyl radical in photosystem II.

Two symmetrically positioned redox active tyrosine residues are present in the photosystem II (PSII) reaction center. One of them, TyrZ, is oxidized in the ns-micros time scale by P680+ and reduced rapidly (micros to ms) by electrons from the Mn complex. The other one, TyrD, is stable in its oxidized form and seems to play no direct role in enzyme function. Here, we have studied electron donation from these tyrosines to the chlorophyll cation (P680+) in Mn-depleted PSII from plants and cyanobacteria. In particular, a mutant lacking TyrZ was used to investigate electron donation from TyrD. By using EPR and time-resolved absorption spectroscopy, we show that reduced TyrD is capable of donating an electron to P680+ with t1/2 approximately equal to 190 ns at pH 8.5 in approximately half of the centers. This rate is approximately 10(5) times faster than was previously thought and similar to the TyrZ donation rate in Mn-depleted wild-type PSII (pH 8.5). Some earlier arguments put forward to rationalize the supposedly slow electron donation from TyrD (compared with that from TyrZ) can be reassessed. At pH 6.5, TyrZ (t1/2 = 2-10 micros) donates much faster to P680+ than does TyrD (t1/2 > 150 micros). These different rates may reflect the different fates of the proton released from the respective tyrosines upon oxidation. The rapid rate of electron donation from TyrD requires at least partial localization of P680+ on the chlorophyll (PD2) that is located on the D2 side of the reaction center.

Photosynthetic water oxidation in Synechocystis sp. PCC6803: mutations D1-E189K, R and Q are without influence on electron transfer at the donor side of photosystem II.

The oxygen-evolving manganese cluster (OEC) of photosynthesis is oxidised by the photochemically generated primary oxidant (P(+*)(680)) of photosystem II via a tyrosine residue (Y(Z), Tyr161 on the D1 subunit of Synechocystis sp. PCC6803). The redox span between these components is rather small and probably tuned by protonic equilibria. The very efficient electron transfer from Y(Z) to P(+*)(680) in nanoseconds requires the intactness of a hydrogen bonded network involving Y(Z), D1-His190, and presumably D1-Glu189. We studied photosystem II core particles from photoautotrophic mutants where the residue D1-E189 was replaced by glutamine, arginine and lysine which were expected to electrostatically differ from the glutamate in the wild-type (WT). Surprisingly, the rates of electron transfer from Y(Z) to P(+*)(680) as well as from the OEC to Y(ox)(Z) were the same as in the WT. With the generally assumed proximity between D1-His190 (and thus D1-Glu189) and Y(Z), the lack of any influence on the electron transfer around Y(Z) straightforwardly implies a strongly hydrophobic environment forcing Glu (acid) and Lys, Arg (basic) at position D1-189 into electro-neutrality. As one alternative, D1-Glu189 could be located at such a large distance from the OEC, Y(Z) and P(+*)(680) that a charge on D1-189X does not influence the electron transfer. This seems less likely in the light of the drastic influence of its direct neighbour, D1-His190, on Y(Z) function. Another alternative is that D1-Glu189 is negatively charged, but is located in a cluster of acid/base groups that compensates for an alteration of charge at position 189, leaving the overall net charge unchanged in the Gln, Lys, and Arg mutants.

Amino acid residues that modulate the properties of tyrosine Y(Z) and the manganese cluster in the water oxidizing complex of photosystem II.

The catalytic site for photosynthetic water oxidation is embedded in a protein matrix consisting of nearly 30 different polypeptides. Residues from several of these polypeptides modulate the properties of the tetrameric Mn cluster and the redox-active tyrosine residue, Y(Z), that are located at the catalytic site. However, most or all of the residues that interact directly with Y(Z) and the Mn cluster appear to be contributed by the D1 polypeptide. This review summarizes our knowledge of the environments of Y(Z) and the Mn cluster as obtained from the introduction of site-directed, deletion, and other mutations into the photosystem II polypeptides of the cyanobacterium Synechocystis sp. PCC 6803 and the green alga Chlamydomonas reinhardtii.

Mobility of antimony in soil and its availability to plants.

In a historical mining area residual material has been filled on land and these locations are used today as agricultural soils or house gardens. The antimony concentrations in these soils are up to 500 mg/kg. Antimony transfer into 19 vegetable and crop species was investigated. In grain and other storage organs up to 0.09 mg Sb/kg were found, whereas maximum antimony concentrations in shoots and leaves were determined to be 0.34 mg Sb/kg and 2.2 mg Sb/kg, respectively. Despite the high antimony contamination of the soils, concentrations in the investigated plants in general corresponded to concentrations only reported for uncontaminated soils. NH4NO3 extraction of some of the soils indicated that the mobile fraction of antimony present was only 0.06-0.59%. In contrast, in leaves of spinach grown under controlled conditions in soils with a high mobile antimony content an accumulation of the element could be observed: a maximum value of 399 mg Sb/kg was detected, and a correlation between the mobile fraction in the soils and antimony in leaves was found.

Effects of halone 1301 on Lepidium sativum, Petunia hybrida and Phaseolus vulgaris.

Halone 1301 belongs to a group of widely used fire repellants. Although banned in several countries, the production has still not been discontinued, and thus hazards due to use or spill can be expected. The study reports on effects of the halone 1301 on three plant species frequently used for bioindication studies: Lepidium sativum (mouse-ear cress), Phaseolus vulgaris (bush bean) and Petunia hybrida. Plants were exposed to 1 ppbv of the gas in ambient air under controlled conditions for 18 days (L. sativum), and 45 days (P. vulgaris, P. hybrida), respectively. None of the plants showed visible stress symptoms. Chlorophylls in cress and petunia were unaffected whereas in beans significant changes of the photosynthetic pigments were observed. Photosynthesis and gas exchange of bean plants were monitored during the experiment, and a lowering of transpiration was noticed. In all investigated plants, protein contents declined significantly, but despite this reduction, activity of the glutathione S-transferases (GST) increased strongly in bean and petunia. The significance of this reaction as detoxification step is discussed.

Glutamate 189 of the D1 polypeptide modulates the magnetic and redox properties of the manganese cluster and tyrosine Y(Z) in photosystem II.

Recent models for water oxidation in photosystem II postulate that the tyrosine Y(Z) radical, Y(Z)(*), abstracts both an electron and a proton from the Mn cluster during one or more steps in the catalytic cycle. This coupling of proton- and electron-transfer events is postulated to provide the necessary driving force for oxidizing the Mn cluster in its higher oxidation states. The formation of Y(Z)(*) requires the deprotonation of Y(Z) by His190 of the D1 polypeptide. For Y(Z)(*) to abstract both an electron and a proton from the Mn cluster, the proton abstracted from Y(Z) must be transferred rapidly from D1-His190 to the lumenal surface via one or more proton-transfer pathways. The proton acceptor for D1-His190 has been proposed to be either Glu189 of the D1 polypeptide or a group positioned by this residue. To further define the role of D1-Glu189, 17 D1-Glu189 mutations were constructed in the cyanobacterium Synechocystis sp. PCC 6803. Several of these mutants are of particular interest because they appear to assemble Mn clusters in 70-80% of reaction centers in vivo, but evolve no O(2). The EPR and electron-transfer properties of PSII particles isolated from the D1-E189Q, D1-E189L, D1-E189D, D1-E189N, D1-E189H, D1-E189G, and D1-E189S mutants were examined. Intact PSII particles isolated from mutants that evolved no O(2) also exhibited no S(1) or S(2) state multiline EPR signals and were unable to advance beyond an altered Y(Z)(*)S(2) state, as shown by the accumulation of narrow "split" EPR signals under multiple turnover conditions. In the D1-E189G and D1-E189S mutants, the quantum yield for oxidizing the S(1) state Mn cluster was very low, corresponding to a > or =1400-fold slowing of the rate of Mn oxidation by Y(Z)(*). In Mn-depleted D1-Glu189 mutant PSII particles, charge recombination between Q(A)(*)(-) and Y(Z)(*) in the mutants was accelerated, showing that the mutations alter the redox properties of Y(Z) in addition to those of the Mn cluster. These results are consistent with D1-Glu189 participating in a network of hydrogen bonds that modulates the properties of both Y(Z) and the Mn cluster and are consistent with proposals that D1-Glu189 positions a group that accepts a proton from D1-His190.

Degradation of the Photosystem II D1 and D2 proteins in different strains of the cyanobacterium Synechocytis PCC 6803 varying with respect to the type and level of psbA transcript.

The turnover of the D1 and D2 proteins of Photosystem II (PSII) has been investigated by pulse-chase radiolabeling in several strains of the cyanobacterium Synechocystis PCC 6803 containing different types and levels of the psbA transcript. Strains lacking psbA1 and psbA3 gene and containing high levels of the psbA2 transcript showed the selective synthesis of D1 whose degradation could be slowed down by the protein synthesis inhibitor lincomycin. In contrast, in strains containing just the psbA3 gene, the intensity of the D1 protein labeling was lower and labeling of the D2 and CP43 proteins was stimulated in comparison to the psbA2-containing strains. In addition, the rate and selectivity of the D1 degradation and its dependence on the presence of lincomycin was proportional to the level of the psbA3 transcript in the particular strain. Consequently, there was parallel, lincomycin-independent and slowed-down breakdown of the D1 and D2 proteins in strains with the lowest level of psbA3 transcript. These results are discussed in terms of a model in which the rate of D1 and D2 degradation in cyanobacteria is affected not only by the rate of PSII photodamage, but also by the availability of newly synthesized D1 protein. Moreover, the comparison of the non-oxygen-evolving D1 mutants D170A** and Y161F*** differing by the presence of tyrosine Z has indicated a minor role of the oxidized form of this secondary PSII electron donor in the donor side mechanism of D1 and D2 protein breakdown.

Histidine 332 of the D1 polypeptide modulates the magnetic and redox properties of the manganese cluster and tyrosine Y(Z) in photosystem II.

An electron spin-echo envelope modulation study [Tang, X.-S., Diner, B. A., Larsen, B. S., Gilchrist, M. L., Jr., Lorigan, G. A., and Britt, R. D. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 704-708] and a recent Fourier transform infrared study [Noguchi, T., Inoue, Y., and Tang, X.-S. (1999) Biochemistry 38, 10187-10195], both conducted with [(15)N]histidine-labeled photosystem II particles, show that at least one histidine residue coordinates the O(2)-evolving Mn cluster in photosystem II. Evidence obtained from site-directed mutagenesis studies suggests that one of these residues may be His332 of the D1 polypeptide. The mutation D1-H332E is of particular interest because cells of the cyanobacterium Synechocystis sp. PCC 6803 that contain this mutation evolve no O(2) but appear to assemble Mn clusters in nearly all photosystem II reaction centers [Chu, H.-A., Nguyen, A. P. , and Debus, R. J. (1995) Biochemistry 34, 5859-5882]. Photosystem II particles isolated from the Synechocystis D1-H332E mutant are characterized in this study. Intact D1-H332E photosystem II particles exhibit an altered S(2) state multiline EPR signal that has more hyperfine lines and narrower splittings than the S(2) state multiline EPR signal observed in wild-type PSII particles. However, the quantum yield for oxidizing the S(1) state Mn cluster is very low, corresponding to an 8000-fold slowing of the rate of Mn oxidation by Y(Z)(*), and the temperature threshold for forming the S(2) state is approximately 100 K higher than in wild-type PSII preparations. Furthermore, the D1-H332E PSII particles are unable to advance beyond the Y(Z)(*)S(2) state, as shown by the accumulation of a narrow "split" EPR signal under multiple turnover conditions. In Mn-depleted photosystem II particles, charge recombination between Q(A)(*)(-) and Y(Z)(*) in D1-H332E is accelerated in comparison to wild-type, showing that the mutation alters the redox properties of Y(Z) in addition to those of the Mn cluster. These results are consistent with D1-His332 being located near the Mn-Y(Z) complex and perhaps ligating Mn.

Role of D1-His190 in the proton-coupled oxidation of tyrosine YZ in manganese-depleted photosystem II.

To further characterize the role of D1-His190 in the oxidation of tyrosine Y(Z) in photosystem II, the pH dependence of P(680)(*)()(+) reduction was measured in H190A and Mn-depleted wild-type PSII particles isolated from the cyanobacterium, Synechocystis sp. PCC 6803. Measurements were conducted in the presence and absence of imidazole and other small organic bases. In H190A PSII particles, rapid reduction of P(680)(*)()(+) attributed to electron transfer from Y(Z) increased dramatically above pH 9, with an apparent pK(A) of approximately 10.3. In the presence of ethanolamine and imidazole, this dramatic increase occurred at lower pH values, with the efficiency of Y(Z) oxidation correlating with the solution pK(A) value of the added base. We conclude that the pK(A) of Y(Z) is approximately 10.3 in D1-H190A PSII particles. In Mn-depleted wild-type PSII particles, P(680)(*)()(+) reduction was accelerated by all exogenous bases examined (substituted imidazoles, histidine, Tris, and 1,4-diazabicyclo[2.2.2]octane). We conclude that Y(Z) is solvent accessible in Mn-depleted wild-type PSII particles and that its pK(A) is near that of tyrosine in solution. In Mn-depleted wild-type PSII particles, over 80% of the kinetics of P(680)(*)()(+) reduction after a flash could be described by three kinetic components. The individual rate constants of these components varied slightly with pH, but their relative proportions varied dramatically with pH, showing apparent pK(A) values of 7.5 and 6.25 (6.9 and 5.8 in the presence of Ca(2+) and Mg(2+) ions). An additional pK(A) value (pK(A) < 4.5) may also be present. To describe these data, we propose (1) the pK(A) of His190 is 6.9-7.5, depending on buffer ions, (2) the deprotonation of Y(Z) is facilitated by the transient formation of a either a hydrogen bond or a hydrogen-bonded water bridge between Y(Z) and D1-His190, and (3) when protonated, D1-His190 interacts with nearby residues having pK(A) values near 6 and 4. Because Y(Z) and D1-His190 are located near the Mn cluster, these residues may interact with the Mn cluster in the intact system.

Impact of mutations within the putative Ca2+-binding lumenal interhelical a-b loop of the photosystem II D1 protein on the kinetics of photoactivation and H2O-oxidation in Synechocystis sp. PCC6803.

Mutations D1-D59N and D1-D61E in the putative Ca2+-binding lumenal interhelical a-b loop of the photosystem II (PSII) D1 protein [Chu, H. A., Nguyen, A. P., and Debus (1995), Biochemistry 34, 5839-5858] were further characterized in terms of S-state cycling and photoactivation. Bare platinum electrode measurements of centrifugally deposited O2-evolving membranes isolated from the a-b loop mutants demonstrated a retarded appearance of O2 following single turnover flashes, although not to the extent of retardation seen in the Deltapsb0 mutant, which lacks the extrinsic manganese-stabilizing protein (MSP). Double flash measurements indicate that retarded O2 release in mutants coincides with a decrease in overall PSII turnover during the S3-[S4]-S0 transition. S2 and S3 decay measurements in the isolated membranes indicate that D1-D59N and D1-D61E have faster decays of these higher S-states in contrast to slowed decays in the Deltapsb0 mutant. Measurements of the flash interval dependence of photoactivation indicate that intermediates of photoactivation [light-dependent assembly of the (Mn)4 complex] are highly destabilized in the a-b loop mutants compared to both DeltapsbO and the wild-type: flash intervals of greater than 2 s result in the nearly complete decay of unstable photointermediate(s) in the D1-D59N and D1-D61E samples, whereas a similar loss does not occur until intervals even greater than 10 s in the DeltapsbO and wild-type samples. These results are consistent with a role for the residues D1-D59 and D1-D61 in modulating the redox properties of the higher S-states and, also, possibly in the binding the calcium ion involved in photoactivation.

Oxygenic photosystem II: the mutation D1-D61N in Synechocystis sp. PCC 6803 retards S-state transitions without affecting electron transfer from YZ to P680+.

Photosynthetic oxygen evolution is powered by photosystem II (PSII), in particular by the oxidized chl a-aggregate P680+, and catalyzed by the oxygen-evolving complex (Mn4X-entity) as well as a tyrosine residue (YZ). The role of particular amino acids as cofactors of electron and proton transfer or as modulators of the activity is still ill-defined. The effects of single-site mutations at the donor side of PSII on the partial reactions of water oxidation have been primarily studied in whole cells. Because of better signal-to-noise in oxygen-evolving core preparations more detailed information on the electronic, protonic, and electrostatic events is expected from studies with such material. We investigated cells and oxygen-evolving core preparations from the wildtype of Synechocystis sp. PCC 6803 and point-mutants of D1-D61. In cells, oxygen-release was slowed drastically in D61A (8-fold) and D61N (10-fold) compared to WT, whereas it remained unchanged in D61E within the time resolution of the measurements. In core preparations, the S1 --> S2 and S2 --> S3 transitions were slowed approximately 2-fold in D61N compared to WT. However, the nanosecond components of electron transfer from YZ to P680+ were unchanged in the same mutant. We conclude that substitution of a neutral residue for D1-D61 selectively affects electron-transfer events on the donor side of YZ.

Structure, stability, and development of young children's self-concepts: a multicohort-multioccasion study.

A new, individual administration procedure for assessing multiple dimensions of self-concept for young children 5-8 years of age (Marsh, Craven, & Debus) was the basis of this study. We expanded this application in a multicohort-multioccasion (MCMO) study that provides simultaneous multicohort comparisons (cross-sectional comparisons of different age cohorts) and longitudinal comparisons of the same children on multiple occasions. There was reasonable support for predictions that reliability, stability, factor structure, and the distinctiveness of the SDQ factors would improve with age (a between-group age cohort comparison) and from 1 year to the next (a longitudinal comparison), and that small gender differences were reasonably stable over age. Consistent with the proposal that children's self-perceptions become more realistic with age, Time 1 (T1) teacher ratings were more highly correlated with student self-ratings at T2 than T1 and contributed to the prediction of T2 self-concept beyond effects mediated by T1 self-concepts. The results support and expand the surprisingly good support for the multidimensionality of self-concept responses for very young children using this procedure.

Role of D1-His190 in proton-coupled electron transfer reactions in photosystem II: a chemical complementation study.

Recent models for water oxidation in photosystem II propose that His190 of the D1 polypeptide facilitates electron transfer from tyrosine YZ to P680+ by accepting the hydroxyl proton from YZ. To test these models, and to further define the role of D1-His190 in the proton-coupled electron transfer reactions of PSII, the rates of P680+ reduction, YZ oxidation, QA- oxidation, and YZ* reduction were measured in PSII particles isolated from several D1-His190 mutants constructed in the cyanobacterium Synechocystis sp. PCC 6803. These measurements were conducted in the absence and presence of imidazole and other small organic bases. In all mutants examined, the rates of P680+ reduction, YZ oxidation, and YZ* reduction after a single flash were slowed dramatically and the rate of QA- oxidation was accelerated to values consistent with the reduction of P680+ by QA- rather than by YZ. There appeared to be little correlation between these rates and the nature of the residue substituted for D1-His190. However, in nearly all mutants examined, the rates of P680+ reduction, YZ oxidation, and YZ* reduction were accelerated dramatically in the presence of imidazole and other small organic bases (e.g., methyl-substituted imidazoles, histidine, methylamine, ethanolamine, and TRIS). In addition, the rate of QA- oxidation was decelerated substantially. For example, in the presence of 100 mM imidazole, the rate of electron transfer from YZ to P680+ in most D1-His190 mutants increased 26-87-fold. Furthermore, in the presence of 5 mM imidazole, the rate of YZ* reduction in the D1-His190 mutants increased to values comparable to that of Mn-depleted wild-type PSII particles in the absence of imidazole. On the basis of these results, we conclude that D1-His190 is the immediate proton acceptor for YZ and that the hydroxyl proton of YZ remains bound to D1-His190 during the lifetime of YZ*, thereby facilitating the reduction of YZ*.

Assessment of the ecotoxic potential of soil contaminants by using a soil-algae test.

To assess the ecotoxic potential of soil contaminants, a test with the soil alga Chlorococcum infusionum has been developed, enabling investigations of soil pollutions with soluble and fairly soluble chemicals. Three soil types artificially contaminated with Sb compounds and five soils from a historical mining area, which were highly polluted with Sb, As, Hg, and Cu, were used as test soils. For antimony, EC50 values from 125 mg/kg up to > 1000 mg/kg, depending on soil type, were determined. Two of five soils from the mining area caused toxic effects. Additionally, aqueous extracts of all soils were exposed in established tests (daphnid, alga, bacterium). In contrast with the soil-algae test, no toxic effects were found. Aquatic tests with SbO/K tartrate were performed to point out the toxicity of antimony. The following EC50 values in milligrams of Sb per liter were determined: Scenedesmus subspicatus, 59 mg/liter; Chlorococcum infusionum, 43 mg/liter; Daphnia magna, 8 mg/liter; and Vibrio fisheri, 7 mg/liter.

The 23 and 17 kDa extrinsic proteins of photosystem II modulate the magnetic properties of the S1-state manganese cluster.

An S1-state parallel polarization "multiline" EPR signal arising from the oxygen-evolving complex has been detected in spinach (PSII) membrane and core preparations depleted of the 23 and 17 kDa extrinsic polypeptides, but retaining the 33 kDa extrinsic protein. This S1-state multiline signal, with an effective g value of 12 and at least 18 hyperfine lines, has previously been detected only in PSII preparations from the cyanobacterium sp. Synechocystis sp. PCC6803 [Campbell, K. A., Peloquin, J. M., Pham, D. P., Debus, R. J., and Britt, R. D. (1998) J. Am. Chem. Soc. 120, 447-448]. It is absent in PSII spinach membrane and core preparations that either fully retain or completely lack the 33, 23, and 17 kDa extrinsic proteins. The S1-state multiline signal detected in spinach PSII cores and membranes has the same effective g value and hyperfine spacing as the signal detected in Synechocystis PSII particles. This signal provides direct evidence for the influence of the extrinsic PSII proteins on the magnetic properties of the Mn cluster.

Self-reports of mathematics self-concept and educational outcomes: the roles of ego-dimensions and self-consciousness.

BACKGROUND: There is a need for research to (a) explore more fully the academic outcomes that follow from under-/over-rating of self-concept and (b) identify factors that predict the nature of self-reports of self-concept as well as under- and over-rating of this self-concept. AIMS: The study examines the link between students' self-appraisals of both mathematics self-concept and under-/over-rating of this self-concept and educational outcomes in mathematics such as achievement and motivation (future plans for mathematics). Ego-dimensions (ego-orientation and competence-valuation) and public self-consciousness were examined as two factors that might contribute to predicting these self-appraisals. SAMPLE: Findings are drawn from a sample of 382 male and female high school students ranging in age from 14 to 16 years. METHODS: Students responded to a questionnaire (at Time 1) that assessed self-concept, motivation orientation, competence-valuation, self-consciousness, and mathematics motivation. Teachers rated each student using a brief mathematics self-concept scale. RESULTS: Higher mathematics self-concept and over-rating of this self-concept were predictive of higher levels of mathematics motivation and later mathematics achievement (Time 2). Findings also indicate that ego-orientation and competence-valuation are positively associated with mathematics self-concept and over-rating, whilst public self-consciousness negatively predicts mathematics self-concept and is also associated with a tendency to under-rate oneself in this domain.

Biodegradability of fluorinated surfactants under aerobic and anaerobic conditions.

The "ready biodegradability" of three fluorinated surfactants was determined under aerobic and anaerobic conditions. Surfactant 1, a solution of a fluorinated surfactant in water, was easily degradable under both aerobic and anaerobic conditions during the incubation periods of 28 and 60 days, respectively. Surfactant 2, a nonionic fluorinated surfactant, was degraded under aerobic conditions in a range of 35-77% during 28 days depending on the source of activated sludge. Aerobic degradation was inhibited by the nitrification-inhibitor dicyandiamide indicating that ammonium oxidizing bacteria may play a role in degradation of surfactant 2. Under anaerobic conditions surfactant 2 was not degraded. Surfactant 3, an anionic fluorinated surfactant, was degraded neither under aerobic nor under anaerobic conditions. Under anaerobic conditions, surfactant 3 inhibited the methane production rate of sludge from a digester. The EC50, i.e. the concentration of surfactant 3 that inhibited 50% of methanogenesis, was determined at 160 mg/l.