Distinct Patterns of Blood Cytokines Beyond a Cytokine Storm Predict Mortality in COVID-19

Background

COVID-19 comprises several severity stages ranging from oligosymptomatic disease to multi-organ failure and fatal outcomes. The mechanisms why COVID-19 is a mild disease in some patients and progresses to a severe multi-organ and often fatal disease with respiratory failure are not known. Biomarkers that predict the course of disease are urgently needed. The aim of this study was to evaluate a large spectrum of established laboratory measurements.

Patients and Methods

Patients from the prospective PULMPOHOM and CORSAAR studies were recruited and comprised 35 patients with COVID-19, 23 with conventional pneumonia, and 28 control patients undergoing elective non-pulmonary surgery. Venous blood was used to measure the serum concentrations of 79 proteins by Luminex multiplex immunoassay technology. Distribution of biomarkers between groups and association with disease severity and outcomes were analyzed.

Results

The biomarker profiles between the three groups differed significantly with elevation of specific proteins specific for the respective conditions. Several biomarkers correlated significantly with disease severity and death. Uniform manifold approximation and projection (UMAP) analysis revealed a significant separation of the three disease groups and separated between survivors and deceased patients. Different models were developed to predict mortality based on the baseline measurements of several protein markers. A score combining IL-1ra, IL-8, IL-10, MCP-1, SCF and CA-9 was associated with significantly higher mortality (AUC 0.929).

Discussion

Several newly identified blood markers were significantly increased in patients with severe COVID-19 (AAT, EN-RAGE, myoglobin, SAP, TIMP-1, vWF, decorin) or in patients that died (IL-1ra, IL-8, IL-10, MCP-1, SCF, CA-9). The use of established assay technologies allows for rapid translation into clinical practice.

Efficacy and safety of pharmacotherapy for Alzheimer's disease and for behavioural and psychological symptoms of dementia in older patients with moderate and severe functional impairments: a systematic review of controlled trials

BACKGROUND

Many patients with Alzheimer's disease (AD) are physically frail or have substantial functional impairments. There is growing evidence that such patients are at higher risk for medication-induced adverse events. Furthermore, frailty seems to be more predictive of poor clinical outcomes than chronological age alone. To our knowledge, no systematic review of clinical trials examining drug therapy of AD or behavioural and psychological symptoms of dementia (BPSD) has specifically focused on the topic of physical frailty. Our objective was to evaluate the efficacy and safety of pharmacotherapy in AD patients with frailty or significant functional impairments.

METHODS

We performed a systematic literature search in MEDLINE, Embase and the Cochrane Central Register of Controlled Trials (CENTRAL) for randomized controlled trials (RCTs) of drug therapy of AD and BPSD in patients with significant functional impairments according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and Cochrane research criteria. Significant functionally impaired patient populations were identified using the recommendations of the Medication and Quality of Life in frail older persons (MedQoL) Research Group. Screening, selection of studies, data extraction and risk of bias assessment were performed independently by two reviewers. Outcomes including functional status, cognitive function, changes in BPSD symptoms, clinical global impression and quality of life were analysed. For assessing harm, we assessed adverse events, drop-outs as a proxy for treatment tolerability and death. Results were analysed according to Cochrane standards and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

RESULTS

Of 45,045 search results, 38,447 abstracts and 187 full texts were screened, and finally, 10 RCTs were included in the systematic review. Selected articles evaluated pharmacotherapy with acetylcholinesterase-inhibitors (AChEI), anticonvulsants, antidepressants and antipsychotics. Studies of AChEIs suggested that patients with significant functional impairments had slight but significant improvements in cognition and that AChEIs were generally well tolerated. Studies of antidepressants did not show significant improvements in depressive symptoms. Antipsychotics and anticonvulsants showed small effects on some BPSD items but also higher rates of adverse events. However, due to the very small number of identified trials, the quality of evidence for all outcomes was low to very low. Overall, the small number of eligible studies demonstrates that significantly functional impaired older patients have not been adequately taken into consideration in most clinical trials investigating drug therapy of AD and BPSD.

CONCLUSION

Due to lack of evidence, it is not possible to give specific recommendations for drug therapy of AD and BSPD in frail older patients or older patients with significant functional impairments. Therefore, clinical trials focussing on frail older adults are urgently required. A standardized approach to physical frailty in future clinical studies is highly desirable.

Ca2+ effects on Fe(II) interactions with Mn-binding sites in Mn-depleted oxygen-evolving complexes of photosystem II and on Fe replacement of Mn in Mn-containing, Ca-depleted complexes

Fe(II) cations bind with high efficiency and specificity at the high-affinity (HA), Mn-binding site (termed the "blocking effect" since Fe blocks further electron donation to the site) of the oxygen-evolving complex (OEC) in Mn-depleted, photosystem II (PSII) membrane fragments (Semin et al. in Biochemistry 41:5854, 2002). Furthermore, Fe(II) cations can substitute for 1 or 2Mn cations (pH dependent) in Ca-depleted PSII membranes (Semin et al. in Journal of Bioenergetics and Biomembranes 48:227, 2016; Semin et al. in Journal of Photochemistry and Photobiology B 178:192, 2018). In the current study, we examined the effect of Ca²⁺ cations on the interaction of Fe(II) ions with Mn-depleted [PSII(-Mn)] and Ca-depleted [PSII(-Ca)] photosystem II membranes. We found that Ca²⁺ cations (about 50 mM) inhibit the light-dependent oxidation of Fe(II) (5 µM) by about 25% in PSII(-Mn) membranes, whereas inhibition of the blocking process is greater at about 40%. Blocking of the HA site by Fe cations also decreases the rate of charge recombination between Q_A^- and Y_Z^•+ from t_1/2 = 30 ms to 46 ms. However, Ca²⁺ does not affect the rate during the blocking process. An Fe(II) cation (20 µM) replaces 1Mn cation in the Mn₄CaO₅ catalytic cluster of PSII(-Ca) membranes at pH 5.7 but 2 Mn cations at pH 6.5. In the presence of Ca²⁺ (10 mM) during the substitution process, Fe(II) is not able to extract Mn at pH 5.7 and extracts only 1Mn at pH 6.5 (instead of two without Ca²⁺). Measurements of fluorescence induction kinetics support these observations. Inhibition of Mn substitution with Fe(II) cations in the OEC only occurs with Ca²⁺ and Sr²⁺ cations, which are also able to restore oxygen evolution in PSII(-Ca) samples. Nonactive cations like La³⁺, Ni²⁺, Cd²⁺, and Mg²⁺ have no influence on the replacement of Mn with Fe. These results show that the location and/or ligand composition of one Mn cation in the Mn₄CaO₅ cluster is strongly affected by calcium depletion or rebinding and that bound calcium affects the redox potential of the extractable Mn4 cation in the OEC, making it resistant to reduction.

Substrate Supporting Disc Method for Confirmed Detection of Total Coliforms and E. coli in all Foods: Collaborative Study

The Coli Complete® substrate supporting disc (SSD) method for simultaneous confirmed total coliform count and Escherichia coli determination in all foods was compared with AOAC most probable number (MPN) methods, 966.23 and 966.24. Twenty-nine laboratories participated in this collaborative study in which 6 food types were analyzed. Four food types, raw ground beef, pork sausage, raw liquid milk, and nut meats, were naturally contaminated with coliform bacteria. Two foods, dry egg and fresh frozen vegetables, were seeded with coliforms. Three food types, ground beef, raw liquid milk, and pork sausage, were naturally contaminated with E. coli. Although pork sausage was naturally contaminated, the level was very low (<10/50 g); therefore, additional E. coli were inoculated into 1 lot of this food type. Three food types, nut meats, dry egg, and fresh frozen vegetables, were inoculated with E. coli. For naturally contaminated samples, duplicate determinations were made on 3 separate lots for each food type. For inoculated samples, low, medium, and high contamination levels plus uninoculated control samples were examined in duplicate. Data were analyzed separately for total coliform bacteria and for E. coli. Mean log MPN counts were determined by the SSD method and the appropriate AOAC MPN method. Results were then analyzed for repeatability, reproducibility, and mean log MPN statistical equivalence. Results were statistically equivalent for all total coliform levels in all food types except frozen vegetable and raw nut meat uninoculated control samples and 1 lot of pork sausage where the SSD method produced statistically significant greater numbers. For the E. coli determinations, results were statistically equivalent across all samples and all levels for each food type. The SSD method has been adopted first action by AOAC International for confirmed detection of total coliforms and E. coli in all foods.

Creation of a 3Mn/1Fe cluster in the oxygen-evolving complex of photosystem II and investigation of its functional activity

Extraction of Mn cations from the oxygen-evolving complex (OEC) of Ca-depleted PSII membranes (PSII[-Ca,4Mn]) by reductants like hydroquinone (H₂Q) occurs with lower efficiency at acidic pH (2Mn/reaction center [RC] are extracted at pH5.7) than at neutral pH (3Mn/RC are extracted at pH6.5) [Semin et al. Photosynth. Res. 125 (2015) 95]. Fe(II) also extracts Mn cations from PSII(-Ca,4Mn), but only 2Mn/RC at pH6.5, forming a heteronuclear 2Mn/2Fe cluster [Semin and Seibert, J. Bioenerg. Biomembr. 48 (2016) 227]. Here we investigated the efficiency of Mn extraction by Fe(II) at acidic pH and found that Fe(II) cations can extract only 1Mn/RC from PSII(-Ca,4Mn) membranes at pH 5.7, forming a 3Mn/1Fe cluster. Also we found that the presence of Fe cations in a heteronuclear cluster (2Mn/2Fe) increases the resistance of the remaining Mn cations to H₂Q action, since H₂Q can extract Mn cations from homonuclear Mn clusters of PSII(-Ca,4Mn) and PSII(-Ca,2Mn) membranes but not from the heteronuclear cluster in PSII(-Ca,2Mn,2Fe) membranes. H₂Q also cannot extract Mn from PSII membranes obtained by incubation of PSII(-Ca,4Mn) membranes with Fe(II) cations at pH5.7, which suggests the formation of a heteronuclear 3Mn/1Fe cluster in the OEC. Functional activity of PSII with a 3Mn/1Fe cluster was investigated. PSII preparations with a 3Mn/1Fe cluster in the OEC are able to photoreduce the exogenous electron acceptor 2,6-dichlorophenolindophenol, possibly due to incomplete oxidation of water molecules as is the case with PSII(-Ca,2Mn,2Fe) samples. However, in the contrast to PSII(-Ca,2Mn,2Fe) samples PSII(-Ca,3Mn,1Fe) membranes can evolve O₂ at a low rate in the presence of exogenous Ca²⁺ (at about 27% of the rate of O₂ evolution in native PSII membranes). The explanation for this phenomenon (either water splitting and production of molecular O₂ by the 3Mn/1Fe cluster or apparent O₂ evolution due to minor contamination of PSII(3Mn,1Fe) samples with PSII(-Ca,4Mn) membranes) is discussed.

Deterioration of quality of life is associated with the exacerbation frequency in individuals with alpha-1-antitrypsin deficiency - analysis from the German Registry

Background

Alpha-1-antitrypsin deficiency (AATD) is a rare hereditary disease that is associated with a higher risk to develop chronic obstructive pulmonary disease and liver cirrhosis. Previous cross-sectional studies on AATD individuals have shown a relationship between worse St George’s Respiratory Questionnaire (SGRQ) scores and elevated exacerbation rate or high cigarette consumption. There is a lack of longitudinal data on the relationship between the exacerbation rate and worsening of SGRQ during disease. The aim of this study was to provide not only cross-sectional data but also information about the deterioration in quality of life over a follow-up period up to 7 years (median follow-up period of 3.33 years).

Methods

We investigated questionnaire-based data of the German AATD registry concerning the relationship between SGRQ and exacerbation frequency, smoking history, forced expiratory volume in 1 second (FEV₁) and carbon monoxide diffusion capacity (DLCO) first in cross-sectional analysis and later in longitudinal analysis.

Results

Eight hundred sixty-eight individuals with protease inhibitor ZZ (PiZZ) genotype with an average age of 52.6±12.8 years had an SGRQ score of 45.7±20.6. SGRQ significantly correlated with the exacerbation frequency within the last 2 years (r=0.464; P<0.001), smoking history (r=0.233; P<0.001), FEV₁ (r=−0.436; P<0.001), DLCO (r=−0.333; P<0.001), and patients’ age (r=0.292; P<0.001). Individuals with occupational dust exposure had significantly worse quality of life (P<0.001). Mean annual deterioration of SGRQ in all patients with available follow-up data (n=286) was 1.21±4.45 points per year. Univariate and multivariate analysis showed a significant relationship between worsening of SGRQ/year and exacerbation frequency in the follow-up period (r=0.144; P=0.015).

Conclusion

Worsening of SGRQ is associated with the exacerbation frequency in individuals with PiZZ AATD.

Sex differences in alpha-1-antitrypsin deficiency lung disease-analysis from the German registry

Alpha-1-antitrypsin deficiency (AATD) is a rare condition with clinical manifestations of the lung and the liver. There is evidence that the gender affects the clinical presentation of non-AATD chronic obstructive lung disease (COPD). The aim of this study was to analyze gender-dependent disease pattern in AATD-based COPD. Data from 1066 individuals from the German AATD registry were analyzed by descriptive and analytical statistics. The AAT genotypes comprised 820 individuals with PiZZ (male 56%, female 45%), 109 with PI SZ (male 55%; female 45%), and others (n = 137). A subgroup of 422 patients with available post-bronchodilator FEV1% predicted was analyzed in detail after stratification in spirometric GOLD stages I-IV. The age of the registered individuals is 52.2 ± 13.4 years (male: 51.91 ± 13.86 years; female: 52.76 ± 13.39 years). Female patients with GOLD I-IV showed lower numbers of pack-years and lower BMI. The time between the first symptom and the establishment of the correct diagnosis was significantly longer in female (14.47 ± 16.46 years) as compared to male individuals (12.39 ± - 14.38 years, p = 0.04). In conclusion, the data of the registry allow to characterize the natural course of the disease and highlight differences in the clinical presentation of patients with AATD-dependent COPD.

Explosions of xenon clusters in ultraintense femtosecond x-ray pulses from the LCLS free electron laser

Explosions of large Xe clusters (<N> ~ 11,000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 10(17) W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.

Site energies of active and inactive pheophytins in the reaction center of Photosystem II from Chlamydomonas reinhardtii

It is widely accepted that the primary electron acceptor in various Photosystem II (PSII) reaction center (RC) preparations is pheophytin a (Pheo a) within the D1 protein (Pheo(D1)), while Pheo(D2) (within the D2 protein) is photochemically inactive. The Pheo site energies, however, have remained elusive, due to inherent spectral congestion. While most researchers over the past two decades placed the Q(y)-states of Pheo(D1) and Pheo(D2) bands near 678-684 and 668-672 nm, respectively, recent modeling [Raszewski et al. Biophys. J. 2005, 88, 986 - 998; Cox et al. J. Phys. Chem. B 2009, 113, 12364 - 12374] of the electronic structure of the PSII RC reversed the assignment of the active and inactive Pheos, suggesting that the mean site energy of Pheo(D1) is near 672 nm, whereas Pheo(D2) (~677.5 nm) and Chl(D1) (~680 nm) have the lowest energies (i.e., the Pheo(D2)-dominated exciton is the lowest excited state). In contrast, chemical pigment exchange experiments on isolated RCs suggested that both pheophytins have their Q(y) absorption maxima at 676-680 nm [Germano et al. Biochemistry 2001, 40, 11472 - 11482; Germano et al. Biophys. J. 2004, 86, 1664 - 1672]. To provide more insight into the site energies of both Pheo(D1) and Pheo(D2) (including the corresponding Q(x) transitions, which are often claimed to be degenerate at 543 nm) and to attest that the above two assignments are most likely incorrect, we studied a large number of isolated RC preparations from spinach and wild-type Chlamydomonas reinhardtii (at different levels of intactness) as well as the Chlamydomonas reinhardtii mutant (D2-L209H), in which the active branch Pheo(D1) is genetically replaced with chlorophyll a (Chl a). We show that the Q(x)-/Q(y)-region site energies of Pheo(D1) and Pheo(D2) are ~545/680 nm and ~541.5/670 nm, respectively, in good agreement with our previous assignment [Jankowiak et al. J. Phys. Chem. B 2002, 106, 8803 - 8814]. The latter values should be used to model excitonic structure and excitation energy transfer dynamics of the PSII RCs.

Determination of the primary charge separation rate in isolated photosystem II reaction centers with 500-fs time resolution

We have measured directly the rate of formation of the oxidized chlorophyll a electron donor (P680(+)) and the reduced electron acceptor pheophytin a(-) (Pheoa(-)) following excitation of isolated spinach photosystem II reaction centers at 4 degrees C. The reaction-center complex consists of D(1), D(2), and cytochrome b-559 proteins and was prepared by a procedure that stabilizes the protein complex. Transient absorption difference spectra were measured from 440 to 850 nm as a function of time with 500-fs resolution following 610-nm laser excitation. The formation of P680(+)-Pheoa(-) is indicated by the appearance of a band due to P680(+) at 820 nm and corresponding absorbance changes at 505 and 540 nm due to formation of Pheoa(-). The appearance of the 820-nm band is monoexponential with tau = 3.0 +/- 0.6 ps. The time constant for decay of (1*)P680, the lowest excited singlet state of P680, monitored at 650 nm, is tau = 2.6 +/- 0.6 ps and agrees with that of the appearance of P680(+) within experimental error. Treatment of the photosystem II reaction centers with sodium dithionite and methyl viologen followed by exposure to laser excitation, conditions known to result in accumulation of Pheoa(-), results in formation of a transient absorption spectrum due to (1*)P680. We find no evidence for an electron acceptor that precedes the formation of Pheoa(-).

Oxygen sensitivity of algal H2- production

Photoproduction of H2 by green algae utilizes electrons originating from the photosynthetic oxidation of water and does not require metabolic intermediates. However, algal hydrogenases are extremely sensitive to O(2), which limits their usefulness in future commercial H2-production systems. We designed an experimental technique for the selection of O2-tolerant, H2-producing variants of Chlamydomonas reinhardtii based on the ability of wild-type cells to survive a short (20 min) exposure to metronidazole in the presence of controlled concentrations of O2. The number of survivors depends on the metronidazole concentration, light intensity, preinduction of the hydrogenase, and the presence or absence of O2. Finally, we demonstrate that some of the selected survivors in fact exhibit H2-production capacity that is less sensitive to O2 than the original wild-type population.

The use of a decremental dose regimen in patients treated with a chronic low-dose step-up protocol for WHO Group II anovulation: a prospective randomized multicentre study

BACKGROUND

In women with chronic anovulation, the choice of the FSH starting dose and the modality of subsequent dose adjustments are critical in controlling the risk of overstimulation. The aim of this prospective randomized study was to assess the efficacy and safety of a decremental FSH dose regimen applied once the leading follicle was 10-13 mm in diameter in women treated for WHO Group II anovulation according to a chronic low-dose (CLD; 75 IU FSH for 14 days with 37.5 IU increment) step-up protocol.

METHODS

Two hundred and nine subfertile women were treated with recombinant human FSH (r-hFSH) (Gonal-f) for ovulation induction according to a CLD step-up regimen. When the leading follicle reached a diameter of 10-13 mm, 158 participants were randomized by means of a computer-generated list to receive either the same FSH dose required to achieve the threshold for follicular development (CLD regimen) or half of this FSH dose [sequential (SQ) regimen]. HCG was administered only if not more than three follicles >or=16 mm in diameter were present and/or serum estradiol (E(2)) values were <1200 pg/ml. The primary outcome measure was the number of follicles >or=16 mm in size at the time of hCG administration.

RESULTS

Clinical characteristics and ovarian parameters at the time of randomization were similar in the two groups. Both CLD and SQ protocols achieved similar follicular growth as regards the total number of follicles and medium-sized or mature follicles (>/=16 mm: 1.5 +/- 0.9 versus 1.4 +/- 0.7, respectively). Furthermore, serum E(2) levels were equivalent in the two groups at the time of hCG administration (441 +/- 360 versus 425 +/- 480 pg/ml for CLD and SQ protocols, respectively). The rate of mono-follicular development was identical as well as the percentage of patients who ovulated and achieved pregnancy.

CONCLUSIONS

The results show that the CLD step-up regimen for FSH administration is efficacious and safe for promoting mono-follicular ovulation in women with WHO Group II anovulation. This study confirms that maintaining the same FSH starting dose for 14 days before increasing the dose in step-up regimen is critical to adequately control the risk of over-response. Strict application of CLD regimen should be recommended in women with WHO Group II anovulation.

[Photochemical activity of photosystem II and hydrogen photoproduction in sulfur-deprived Chlamydomonas reinhardtii mutants D1-R323D and D1-R323L]

The role of photosystem II in hydrogen photoproduction by Chlamydomonas reinhardtii cells was studied in mutants with modified D1-protein. In D1-R323D and D1-R323L mutants, the replacement of arginine by aspartate or leucine, respectively, resulted in the disruption of electron transport at the donor side of photosystem II. The rate of oxygen evolution in D1-R323D decreased twice as compared to the pseudo-wild type (pWT), and in D1-R323L no oxygen evolution was detected. The latter mutant was not capable of photoautotrophical growth. The dynamics of changes in oxygen content, the reduction of photosystem II active reaction centers (deltaF/F(1)m), and hydrogen production rate in pWT were found to be similar to the wild type if cultivated under sulfur deprivation in a closed bioreactor. The observed gradual decrease in the deltaF/F(1)m value turned to a sharp drop almost to zero followed by a partial recovery during which the production of hydrogen set in. The transition to the anaerobic phase in D1-R323D cultured in a sulfur-deprived medium occurred earlier than it happened in pWt under the same conditions. However, the partial recovery of photosystem II activity and hydrogen production started at a later time, and the rate of hydrogen production was low. The D1-R323L mutant incapable of oxygen evolution entered the rapidly anaerobiosis but produced no hydrogen. The kinetics of photoinduced redox transitions in P700 was similar in all investigated strains and was not affected by diuron addition. This implies that the mutants had a pool of reducers, which could donate electrons through the quinone pool or cytochrome to photosystem I. However, in D1-R323L mutant lacking the active photosystem II, this condition was not sufficient to support hydrogenase activity.

Identification of genes required for hydrogenase activity in Chlamydomonas reinhardtii

The eukaryotic green alga, Chlamydomonas reinhardtii, produces H(2) under anaerobic conditions, in a reaction catalysed by an [FeFe]-hydrogenase. To identify genes that influence H(2) production in C. reinhardtii, a library of 6000 colonies on agar plates was screened with sensitive chemochromic H(2)-sensor films for clones defective in H(2) production. Two mutants of particular interest were fully characterized. One mutant, hydEF-1, is unable to assemble an active [FeFe]-hydrogenase. This is the first reported C. reinhardtii mutant that is not capable of producing any H(2). The second mutant, sta7-10, is not able to accumulate insoluble starch and has significantly lowered H(2)-photoproduction rates in comparison with the wild-type. In hydEF-1, anaerobiosis induces transcription of the two reported C. reinhardtii hydrogenase genes, HydA1 and HydA2, indicating a normal transcriptional response to anaerobiosis. In contrast, the transcription of both hydrogenase genes in sta7-10 is significantly attenuated.

Approaches to developing biological H(2)-photoproducing organisms and processes

The development of efficient biological systems for the direct photoproduction of H(2) gas from water faces several challenges, the more serious of which is the sensitivity of the H(2)-evolving enzymes (hydrogenases) to O(2), an obligatory by-product of photosynthesis. This high sensitivity is common to both FeFe and NiFe hydrogenases, and is caused by O(2) binding to their respective metallocatalytic sites. This overview describes approaches to (i) molecular engineering of algal FeFe-hydrogenase to prevent O(2) access to its catalytic site; (ii) transform a cyanobacterium with an O(2)-tolerant bacterial NiFe hydrogenase or (c) partially inactivate algal O(2)-evolution activity to create physiologically anaerobiosis and induce hydrogenase expression.

The dependence of algal H2 production on Photosystem II and O2 consumption activities in sulfur-deprived Chlamydomonas reinhardtii cells

Chlamydomonas reinhardtii cultures, deprived of inorganic sulfur, undergo dramatic changes during adaptation to the nutrient stress [Biotechnol. Bioeng. 78 (2002) 731]. When the capacity for Photosystem II (PSII) O(2) evolution decreases below that of respiration, the culture becomes anaerobic [Plant Physiol. 122 (2000) 127]. We demonstrate that (a) the photochemical activity of PSII, monitored by in situ fluorescence, also decreases slowly during the aerobic period; (b) at the exact time of anaerobiosis, the remaining PSII activity is rapidly down regulated; and (c) electron transfer from PSII to PSI abruptly decreases at that point. Shortly thereafter, the PSII photochemical activity is partially restored, and H(2) production starts. Hydrogen production, which lasts for 3-4 days, is catalyzed by an anaerobically induced, reversible hydrogenase. While most of the reductants used directly for H(2) gas photoproduction come from water, the remaining electrons must come from endogenous substrate degradation through the NAD(P)H plastoquinone (PQ) oxido-reductase pathway. We propose that the induced hydrogenase activity provides a sink for electrons in the absence of other alternative pathways, and its operation allows the partial oxidation of intermediate photosynthetic carriers, including the PQ pool, between PSII and PSI. We conclude that the reduced state of this pool, which controls PSII photochemical activity, is one of the main factors regulating H(2) production under sulfur-deprived conditions. Residual O(2) evolved under these conditions is probably consumed mostly by the aerobic oxidation of storage products linked to mitochondrial respiratory processes involving both the cytochrome oxidase and the alternative oxidase. These functions maintain the intracellular anaerobic conditions required to keep the hydrogenase enzyme in the active, induced form.

Pancreatic beta-cells expressing the Arg64 variant of the beta(3)-adrenergic receptor exhibit abnormal insulin secretory activity

The Arg64 beta(3)-adrenergic receptor (beta(3)AR) variant is associated with an earlier age of onset of diabetes and lower levels of insulin secretion in humans. The aims of this study were to investigate whether beta(3)AR is expressed by islet cells, if receptor binding affects insulin secretion and, finally, if the beta(3)AR Arg64 variant induces abnormal insulin secretory activity. Human pancreas extracts were subjected to RT-PCR, Western blotting and immunostaining analyses. DNA sequencing and Western blotting demonstrated that the beta(3)AR gene is transcribed and translated in the human pancreas; immunostaining showed that it is expressed by the islets of Langerhans. Cultured rat beta-cells responded to human beta(3)AR agonists in a dose- and time-dependent manner. Transfection of cultured rat beta-cells with the wild-type human beta(3)AR produced an increased baseline and ligand-dependent insulin secretion compared with parental cells. On the other hand, cells transfected with the Arg64 variant of the beta(3)AR secreted less insulin, both spontaneously and after exposure to human beta(3)AR agonists. Furthermore, while transfection with the wild-type beta(3)AR preserved the glucose-dependent secretion of insulin, expression of the variant receptor rendered the host cells significantly less responsive to glucose. In summary, cells express the beta(3)AR, and its activation contributes to the regulation of insulin secretion. These findings may help explain the low levels of insulin secretion in response to an i.v. glucose tolerance test observed in humans carrying the Arg64 polymorphism.

Microalgae: a green source of renewable H(2)

This article summarizes recent advances in the field of algal hydrogen production. Two fundamental approaches are being developed. One involves the temporal separation of the usually incompatible reactions of O(2) and H(2) production in green algae, and the second involves the use of classical genetics to increase the O(2) tolerance of the reversible hydrogenase enzyme. The economic and environmental impact of a renewable source of H(2) are also discussed.

Insulin response to glucose is lower in individuals homozygous for the Arg 64 variant of the beta-3-adrenergic receptor

Type 2 diabetes mellitus (type 2 DM) is a polygenic disorder with a variable phenotype that includes both insulin resistance and insulin secretory dysfunction. The Arg 64 beta-3-adrenergic receptor variant allele is associated with an earlier age of onset of type 2 DM. The purpose of this study was to examine the in vivo pathophysiology of this variant allele to determine its contribution to the components of glucose metabolism. We used the frequently sampled iv glucose tolerance tests, minimal model analysis, and analysis of covariance to examine age- and fat-mass-adjusted differences among genotypes. The results demonstrate that individuals homozygous for the Arg 64 allele secrete significantly less insulin in response to a glucose infusion (562+/-116 vs. 962+/-94 pmol/microL), have the highest fasting glucose levels (100.4+/-1.9 vs. 92.48+/-1.60 mg/dL), and have lower glucose effectiveness (0.014+/-0.003 vs. 0.019+/-0.002 min(-1)), compared with those homozygous for the Trp 64 allele. This first report of decreased acute insulin release and lower glucose effectiveness in the Arg 64 genotype may help explain the earlier onset of type 2 DM observed in several populations of individuals with the Arg64 beta-3-adrenergic receptor variant allele.

Resonance Raman and surface-enhanced resonance Raman spectra of LH2 antenna complex from Rhodobacter sphaeroides and Ectothiorhodospira sp. excited in the Qx and Qy transitions

Well-resolved vibrational spectra of LH2 complex isolated from two photosynthetic bacteria, Rhodobacter sphaeroides and Ectothiorhodospira sp., were obtained using surface-enhanced resonance Raman scattering (SERRS) exciting into the Qx and the Qy transitions of bacteriochlorophyll a. High-quality SERRS spectra in the Qy region were accessible because the strong fluorescence background was quenched near the roughened Ag surface. A comparison of the spectra obtained with 590 nm and 752 nm excitation in the mid- and low-frequency regions revealed spectral differences between the two LH2 complexes as well as between the LH2 complexes and isolated bacteriochlorophyll a. Because peripheral modes of pigments contribute mainly to the low-frequency spectral region, frequencies and intensities of many vibrational bands in this region are affected by interactions with the protein. The results demonstrate that the microenvironment surrounding the pigments within the two LH2 complexes is somewhat different, despite the fact that the complexes exhibit similar electronic absorption spectra. These differences are most probably due to specific pigment-pigment and pigment-protein interactions within the LH2 complexes, and the approach might be useful for addressing subtle static and dynamic structural variances between pigment-protein complexes from different sources or in complexes altered chemically or genetically.

Sustained photobiological hydrogen gas production upon reversible inactivation of oxygen evolution in the green alga Chlamydomonas reinhardtii

The work describes a novel approach for sustained photobiological production of H(2) gas via the reversible hydrogenase pathway in the green alga Chlamydomonas reinhardtii. This single-organism, two-stage H(2) production method circumvents the severe O(2) sensitivity of the reversible hydrogenase by temporally separating photosynthetic O(2) evolution and carbon accumulation (stage 1) from the consumption of cellular metabolites and concomitant H(2) production (stage 2). A transition from stage 1 to stage 2 was effected upon S deprivation of the culture, which reversibly inactivated photosystem II (PSII) and O(2) evolution. Under these conditions, oxidative respiration by the cells in the light depleted O(2) and caused anaerobiosis in the culture, which was necessary and sufficient for the induction of the reversible hydrogenase. Subsequently, sustained cellular H(2) gas production was observed in the light but not in the dark. The mechanism of H(2) production entailed protein consumption and electron transport from endogenous substrate to the cytochrome b(6)-f and PSI complexes in the chloroplast thylakoids. Light absorption by PSI was required for H(2) evolution, suggesting that photoreduction of ferredoxin is followed by electron donation to the reversible hydrogenase. The latter catalyzes the reduction of protons to molecular H(2) in the chloroplast stroma.

Tumor necrosis factor-alpha-238 and -308 polymorphisms do not associated with traits related to obesity and insulin resistance

Tumor necrosis factor-alpha (TNF-alpha) is expressed primarily in adipocytes, and elevated levels of this cytokine have been linked to obesity and insulin resistance. The purpose of this investigation was to test whether the TNF-alpha-308 polymorphism (previously linked to insulin resistance and increased leptin levels) and the TNF-alpha-238 polymorphism (linked to decreased insulin resistance) were associated with insulin resistance or obesity-related traits in 424 subjects self-referred to the Johns Hopkins Weight Management Center (JHWMC). There were no differences in allele frequencies of either polymorphism by obesity category in the JHWMC and a lean control group. Despite previous smaller studies that have linked insulin resistance and the 308 allele, we found no such relationship in the JHWMC population. Instead, homozygotes for this allele had a significantly lower BMI than their counterparts without the polymorphism. In addition, we found no relationship between the 238 polymorphism and BMI, fasting glucose, or log of fasting insulin.

Use of a novel histidyl modifier to probe for residues on Tris-treated photosystem II membrane fragments that may bind functional manganese

In this paper, we investigate the effects of histidyl amino acid modification on high-affinity Mn binding to photosystem II (PSII) using methods similar to those used in the preceding paper [Ghirardi et al. (1998) Biochemistry 37, 0000] for carboxyl amino acid modification. Given the rather low specificity of diethyl pyrocarbonate (DEPC) for histidine modification, we modified Tris-washed PSII membranes with a novel and more specific histidyl modifier, platinum(II) (2,2':6',2"-terpyridine) chloride (Pt-TP). Both the "diphenylcarbazide (DPC)-inhibition assay" and single-turnover flash approaches were used. The concentration dependence of Pt-TP modification on steady-state measurements shows two types of interactions, each accounting for about half of the full effect. At concentrations <50 microM, Pt-TP modifies mostly histidyls and abolishes half of the observed Mn inhibition of DPC-mediated 2,6-dichlorophenolindophenol (DCIP) photoreduction (equivalent to two high-affinity, Mn-binding ligands). This effect can be blocked by addition of Mn2+ during Pt-TP modification. Double-modification experiments with DEPC and Pt-TP demonstrate that both modifiers affect the same observable histidyl residues in PSII. Above 50 microM, Pt-TP modifies mostly cysteines (or histidines in a more hydrophobic environment) and has an additional effect on the reducing side of PSII that (a) does not involve Mn binding and (b) results in the apparent abolishment of all four of the Mn-binding ligands detected by the DPC-inhibition assay. Single-flash experiments show that histidyl modification does not eliminate the binding of the high-affinity, photooxidizable Mn2+ to Asp170 on D1 (nor does it significantly affect high-affinity DPC photooxidation), but it does decrease the binding affinity (Kd) of that Mn from 0.6 to 1.5 microM, particularly at lower (<50 microM Pt-TP) concentrations. Double-modification experiments also demonstrate that the lower affinity, photooxidizable Mn-binding site, uncovered when the high-affinity site is modified with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC) [see Ghirardi et al. (1998)], is not associated with a histidyl ligand. Three nonphotooxidizable, high-affinity Mn2+ ions bind to a second carboxyl and two histidyl ligands, and these Mn are not photooxidized by a flash even when the ligand to the photooxidizable Mn is modified by EDC. Proteolytic enzyme studies indicate that the two histidyl ligands identified by the DPC-inhibition assay are probably His337 on D1 and His 339 on D2, but His 332 on D1 is not eliminated.

Effects of carboxyl amino acid modification on the properties of the high-affinity, manganese-binding site in photosystem II

Our previous work using the "diphenylcarbazide (DPC)-inhibition assay" has identified four amino acid (two carboxyls and two histidyls) ligands to four Mn2+ bound with high affinity on Tris-washed photosystem II (PSII) membrane fragments [Preston and Seibert (1991) Biochemistry 30, 9615-9624, 9625-9633]. One of the ligands binds a photooxidizable Mn, specifically, and the others bind either nonphotooxidizable Mn2+, Zn2+, or Co2+ [Ghirardi et al. (1996) Biochemistry 35, 1820-1828]. The current paper shows the following: (a) the high-affinity photooxidizable Mn, which donates to the oxidized primary PSII donor (YZ*), is bound to a carboxyl residue with a KM = 1.5 microM or Kd = 0.94 microM in the absence of DPC, and a Ki = 1.3 microM in the presence of DPC (both steady-state and flash approaches were used); (b) if this carboxyl is chemically modified using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC), Mn2+ is photooxidized at a lower affinity (Kd = 25 microM) site that does not involve carboxyl ligands; (c) low-affinity Mn is photooxidized (possibly by YD*, the oxidized form of the alternative PSII donor) with a KM = 220 microM at a completely different site that also requires a carboxyl ligand; (d) photooxidation of high-affinity DPC by YZ* with a KM of 40-42 microM or Kd of 49-58 microM occurs at a site that does not require carboxyl residues; (e) photooxidation of low-affinity DPC with a KM = 1200 microM occurs at a site (possibly near YD) that is not affected by carboxyl modification with EDC. Due to the similarities between the binding of the high-affinity photooxidizable Mn to EDC-treated membranes and to PSII complexes from Asp170D1 mutants [Nixon and Diner (1992) Biochemistry 31, 942-948], we identify its carboxyl residue ligand as Asp170 on D1, one of the reaction-center proteins. The second carboxyl ligand identified using the DPC-inhibition assay binds Mn (but not a photooxidizable one), Zn, or Co ions. At least one of the two histidyl ligands (either His337 on D1 or another unidentified histidyl) that bind nonphotooxidizable, high-affinity Mn2+ also binds Zn2+ and Co2+.

Action of K-crown ether on photosystem II electron transport: characterization of the site of action

We have investigated the inhibitory effect of K-crown (18-crown-6 potassium picrate) on photosystem II (PSII)-enriched membrane fragments and O2-evolving core complexes. K-crown at 2-4 microM inhibits about half the control level of O2-evolution activity in both types of PSII samples. Oxygen-evolution studies demonstrated that the ether works by inactivating the centres and not by interfering with antenna function or energy transfer to the reaction centre. K-crown does not disrupt binding of the extrinsic proteins associated with O2 evolution nor complex with bound Ca2+ or Cl- cofactors, but rather it directly inhibits electron transfer after the tetrameric Mn cluster. Fluorescence studies on active and Tris-treated samples showed that K-crown does not prevent artificial donors from transferring electrons to PSII but like DCMU inhibits on the acceptor side after QA, the primary quinone acceptor. However, the ether is a leaky inhibitor and may also act as a weak donor when the Mn cluster is not present. Oxygen-production experiments using silicomolybdate as an artificial acceptor (which accepts from both pheophytin and QB in PSII membranes) demonstrated that the inhibition is at or near the DCMU site.

Langmuir-Blodgett and X-ray diffraction studies of isolated photosystem II reaction centers in monolayers and multilayers: physical dimensions of the complex

The photosystem II (PSII) reaction center (RC) is a hydrophobic intrinsic protein complex that drives the water-oxidation process of photosynthesis. Unlike the bacterial RC complex, an X-ray crystal structure of the PSII RC is not available. In order to determine the physical dimensions of the isolated PSII RC complex, we applied Langmuir techniques to determine the cross-sectional area of an isolated RC in a condensed monolayer film. Low-angle X-ray diffraction results obtained by examining Langmuir-Blodgett multilayer films of alternating PSII RC/Cd stearate monolayers were used to determine the length (or height; z-direction, perpendicular to the plane of the original membrane) of the complex. The values obtained for a PSII RC monomer were 26 nm2 and 4.8 nm, respectively, and the structural integrity of the RC in the multilayer film was confirmed by several approaches. Assuming a cylindrical-type RC structure, the above dimensions lead to a predicted volume of about 125 nm3. This value is very close to the expected volume of 118 nm3, calculated from the known molecular weight and partial specific volume of the PSII RC proteins. This same type of comparison was also made with the Rhodobacter sphaeroides RC based on published data, and we conclude that the PSII RC is much shorter in length and has a more regular solid geometric structure than the bacterial RC. Furthermore, the above dimensions of the PSII RC and those of PSII core (RC plus proximal antenna) proteins protruding outside the plane of the PSII membrane into the lumenal space as imaged by scanning tunneling microscopy (Seibert, Aust. J. Pl. Physiol. 22, 161-166, 1995) fit easily into the known dimensions of the PSII core complex visualized by others as electron-density projection maps. From this we conclude that the in situ PSII core complex is a dimeric structure containing two copies of the PSII RC.

Photochemical reactions of photosystem II in ethylene glycol

The behavior of photosystem II (PSII) reactions was investigated under conditions of decreasing water content by the addition of increasing concentrations of ethylene glycol (EG). The photosynthetic activities were measured for PSII samples either directly in aqueous solutions of EG or in the standard buffer medium following EG treatment. Several effects on PSII arise upon exposure to EG. Below 50% EG there are no significant irreversible changes, although there is a slowing of the QA-reoxidation kinetics in the presence of EG. At concentrations of 50-70% EG, protein structural changes occur that include the release of the 16, 23, and 33 kDa extrinsic proteins and two of the catalytic Mn ions. For these samples, the capacity for O2 evolution is considerably reduced and the formation of donor side H2O2 is enhanced. In 60% EG, the nanosecond components in the rate of P680+ reduction are converted entirely to microsecond kinetics which upon return of the sample to the standard buffer medium are partially restored, indicating that EG has a reversible, solvent effect on the PSII donor side. At concentrations of EG > 70% chlorophyll fluorescence measurements reveal reversible increases in the FO level concomitant with the generation and disappearance of a 5 microseconds decay component in the P680+ reduction kinetics. This result may indicate a solvent-induced uncoupling of the light harvesting pigment bed from the reaction center complex. As the EG concentration is increased to 80-100%, there is an irreversible loss of the primary charge separation. The use of EG as a cryoprotectant and as a water-miscible organic solvent for PSII is discussed.

Oxygen sensitivity of algal H2- production

Photoproduction of H2 by green algae utilizes electrons originating from the photosynthetic oxidation of water and does not require metabolic intermediates. However, algal hydrogenases are extremely sensitive to O(2), which limits their usefulness in future commercial H2-production systems. We designed an experimental technique for the selection of O2-tolerant, H2-producing variants of Chlamydomonas reinhardtii based on the ability of wild-type cells to survive a short (20 min) exposure to metronidazole in the presence of controlled concentrations of O2. The number of survivors depends on the metronidazole concentration, light intensity, preinduction of the hydrogenase, and the presence or absence of O2. Finally, we demonstrate that some of the selected survivors in fact exhibit H2-production capacity that is less sensitive to O2 than the original wild-type population.

Interactions between diphenylcarbazide, zinc, cobalt, and manganese on the oxidizing side of photosystem II

The inhibition of DPC-mediated DCIP photoreduction by exogenous MnCl2 in Tris-treated photosystem II (PSII) membrane fragments has been used to probe for amino acids on the PSII reaction center proteins, including D1His337, that provide ligands for binding manganese [Preston, C., & Seibert, M. (1990) in Current Research in Photosynthesis (Baltscheffsky, M., Ed.) Vol. I, pp 925-928, Kluwer Academic Publishers, Dordrecht, The Netherlands; Preston, C., & Seibert, M. (1991) Biochemistry 30, 9615-9624 and 9625-9633]. At a concentration of 200 microM, DPC is photooxidized at both a high-affinity and a low-affinity site in PSII at approximately the same initial rate. Addition of 10 microM MnCl2 noncompetitively inhibits DPC photooxidation at the high-affinity site, with a Ki of 1.5 microM, causing a decrease of about 50% in the overall DCIP photoreduction rate. The high-affinity site for Mn binding was deconvoluted into four independent components. In earlier work, the inhibition was attributed to the tight association of either Mn2+ or Mn3+ with the PSII membrane. We report here that inhibition of DPC photooxidation may involve two different types of high-affinity, Mn-binding components: (a) one that is specific for Mn, and (b) others that bind Mn, but may also bind additional divalent cations, such as Zn and Co, that are not photooxidized by PSII. These conclusions are based on the observations that (a) DPC photooxidation can be inhibited by Zn2+ and Co2+; (b) Zn2+ and Co2+ interact with Mn2+ in a nonmutually exclusive manner, suggesting that they may share some binding components with Mn2+; (c) high-affinity Mn2+ (but not Zn2+ or Co2+) inhibition of DPC photooxidation is accompanied by nondecaying fluorescence emission, following a single saturating flash, indicating efficient electron donation by Mn2+ to YZ+; (d) Mn2+ photooxidation in the presence of DPC is not inhibited by Zn2+ or Co2+; and (e) kinetic modeling of the interaction between high-affinity Mn2+ and DPC in PSII indicates inhibition of steady-state Mn2+ photooxidation by DPC, but allows for a single photooxidation of Mn2+. We conclude that Mn inhibition of DPC photooxidation can be used to identify Mn-binding sites of physiological importance, and suggest that the Mn-specific component of the high-affinity, Mn-binding site involves the ligand to the first Mn bound during photoactivation (i.e., Asp170 on D1, as found by other investigators).

Pigment content of D1-D2-cytochrome b559 reaction center preparations after removal of CP47 contamination: an immunological study

Isolated D1-D2-cytochrome b559 photosystem II reaction center preparations with pigment stoichiometry higher than 4 chlorophylls per 2 pheophytins can be contaminated with CP47 proximal antenna complex. Reaction center prepared by a modification of the Nanba-Satoh procedure and containing about 6 chlorophylls per 2 pheophytins showed immuno-cross-reactivity when probed with a monoclonal antibody raised against the CP47 polypeptide. Furthermore, they could be fractionated successfully by Superose-12 sieve chromatography into two different populations. The first few fractions off the column contained a more definitive 435 nm shoulder corresponding to increased chlorophyll content, and showed strong immuno-cross-reactivity with the CP47 antibody. The peak fractions off the column displayed a less prominent 435 nm shoulder, and did not cross-react with the antibody. Moreover, when a 6-chlorophyll preparation was mixed with Sepharose beads coupled to CP47 antibody, the eluted material corresponded to a preparation of about 4 chlorophylls per 2 pheophytins and did not show any cross-reaction with the antibody against CP47. The amount of CP47 protein in the 6-chlorophyll preparation as quantitated using Coomassie Blue staining or from gel blots was sufficient to account for most of the extra 2 chlorophylls. We conclude that D1-D2-cytochrome b559 preparations containing more than 4 chlorophylls per 2 pheophytins can be contaminated with small amounts of CP47-D1-D2-Cyt b559 complex and that native photosystem II reaction centers contain 4 core chlorophylls per 2 pheophytins.

[Arterial and venous alcohol elimination in 10 polytrauma patients]

Alcohol elimination was examined in 10 patients involved in accidents while intoxicated. The influence of trauma, particularly polytrauma resulting in haemorrhage shock and its therapeutic treatment were analysed. The blood alcohol concentrations were determined according to the usual forensic criteria (2 alcohol dehydrogenase and 2 gas chromatography measurements). Observation periods ranged from 3 hours 45 minutes to 12 hours 35 minutes, with blood being drawn at intervals ranging from 45 minutes to 185 minutes (on average 70 minutes). Results of two patients (delta 60 = 0.22/1000/h and 0.28/1000/h) who only had 3 venous drawn and results of a deceased patient from whom only four arterial samples could be obtained (beta 60 = 0.21/1000/h) were disregarded when working out the average values. The blood alcohol curve plateaued in the case of the deceased patient as well as in the case of a patient whose hepatic circulation was curtailed for approximately half an hour during surgery. The blood alcohol curves for the remaining patients for uniformly linear with beta 60 values between 0.17/1000/h and 0.21/1000/h (mean = 0.18/1000/h +/- 0.01) in arterial samples and 0.18/1000/h and 0.21/1000/h (mean = 0.18/1000/h +/- 0.01) in venous samples. Given our results and the existing literature, we feel that retrograde calculations of the BAC can be justified in patients with polytrauma, despite the small number of patients included in the study. Naturally, the usual forensic criteria have to be taken into account, as well as individual situations. Examples that can be mentioned here are liver failure or curtailment of hepatic circulation during surgery.

Femtosecond photodichroism studies of isolated photosystem II reaction centers

Photosynthetic conversion of light energy into chemical potential begins in reaction center protein complexes, where rapid charge separation occurs with nearly unit quantum efficiency. Primary charge separation was studied in isolated photosystem II reaction centers from spinach containing 6 chlorophyll a, 2 pheophytin a (Pheo), 1 cytochrome b559, and 2 beta-carotene molecules. Time-resolved pump-probe kinetic spectroscopy was carried out with 105-fs time resolution and with the pump laser polarized parallel, perpendicular, and at the magic angle (54.7 degrees) relative to the polarized probe beam. The time evolution of the transient absorption changes due to the formation of the oxidized primary electron donor P680+ and the reduced primary electron acceptor Pheo- were measured at 820 nm and 545 nm, respectively. In addition, kinetics were obtained at 680 nm, the wavelength ascribed to the Qy transition of the primary electron donor P680 in the reaction center. At each measured probe wavelength the kinetics of the transient absorption changes can be fit to two major kinetic components. The relative amplitudes of these components are strongly dependent on the polarization of the pump beam relative to that of the probe. At the magic angle, where no photoselection occurs, the amplitude of the 3-ps component, which is indicative of the charge separation, dominates. When the primary electron acceptor Pheo is reduced prior to P680 excitation, the 3-ps component is eliminated.

Slow oxygen release on the first two flashes in chemically stressed Photosystem II membrane fragments results from hydrogen peroxide oxidation

Flash-induced amperometric signals were measured with a Joliot-type O2 rate electrode in spinach Photosystem II (PS II) membrane fragments exposed to very low concentrations of added hydroxylamine or hydrogen peroxide. In both cases 'anomalous O2 signals' were observed on the first two flashes, and oscillating four-flash patterns were observed on subsequent flashes. The anomalous signals were eliminated in the presence of catalase but not EDTA. The rise times of the O2-release kinetics associated with the anomalous signals were slow (ca. 20 ms with NH2OH and ca. 120 ms with H2O2) compared to the kinetics of O2 release on subsequent flashes and in control membranes (3-6 ms). It is proposed that when the intact PS II O2-evolving complex is perturbed with small concentrations of added reductant, H2O2 can gain access and bind to the complex. Bound H2O2 can then reduce lower S states in some centers leading to anomalous O2 signals on the first two flashes. A model is presented to explain both types of anomalous O2 production. Oxygen observed on the third and subsequent flashes is due to the normal photosynthetic O2-evolution process arising from the S3-state. Anomalous O2 production could be a protective mechanism in PS II centers subjected to stress conditions.