The Tragedy of the Commons: Twenty-two years later

Hardin's Tragedy of the Commons model predicts the eventual overexploitation or degradation of all resources used in common. Given this unambiguous prediction, a surprising number of cases exist in which users have been able to restrict access to the resource and establish rules among themselves for its sustainable use. To assess the evidence, we first define common-property resources and present a taxonomy of property-rights regimes in which such resources may be held. Evidence accumulated over the last twenty-two years indicates that private, state, andcommunal property are all potentially viable resource management options. A more complete theory than Hardin's should incorporate institutional arrangements and cultural factors to provide for better analysis and prediction.     

Microbiological coal desulphurization

Sulphur compounds present in coal impose severe limitations on its utilization since sulphur-containing gases emitted into the atmosphere upon direct combustion of coal cause serious environmental pollution problems. Removal of sulphur compounds from coal by microbial action has many advantages over physical and chemical desulphurization methods. The potential use of various microorganisms for the removal of sulphur compounds from coal is presented. Environmental conditions and major process variables affecting the process performance are identified and their possible effects are discussed. Various process schemes for microbial desulphurization (MDS) of coal are suggested. It is concluded that microbial methods have a high potential in removing sulphur compounds from coal. However, more research and development work is needed in this field to overcome present technological problems.     

Misses during water oxidation in photosystem II are S state-dependent

The period of four oscillation of the S state intermediates of the water oxidizing complex in Photosystem II (PSII) is commonly analyzed by the Kok parameters. The important miss factor determines the efficiency for each S transition. Commonly, an equal miss factor has been used in the analysis. We have used EPR signals which probe all S states in the same sample during S cycle advancement. This allows, for the first time, to measure directly the miss parameter for each S state transition. Experiments were performed in PSII membrane preparations from spinach in the presence of electron acceptor at 1 °C and 20 °C. The data show that the miss parameter is different in different transitions and shows different temperature dependence. We found no misses at 1 °C and 10% misses at 20 °C during the S(1)→S(2) transition. The highest miss factor was found in the S(2)→S(3) transition which decreased from 23% to 16% with increasing temperature. For the S(3)→S(0) transition the miss parameter was found to be 7% at 1 °C and decreased to 3% at 20 °C. For the S(0)→S(1) transition the miss parameter was found to be approximately 10% at both temperatures. The contribution from the acceptor side in the form of recombination reactions as well as from the donor side of PSII to the uneven misses is discussed. It is suggested that the different transition efficiency in each S transition partly reflects the chemistry at the CaMn(4)O(5) cluster. That consequently contributes to the uneven misses during S cycle turnover in PSII.     

Antioxidant capacity of Lemna gibba L. exposed to wastewater treatment

In this study, the amounts of antioxidant vitamins (A, E and C), selenium (Se), reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio and malondialdehyde (MDA) that is the indicator of lipid peroxidation were determined in Lemna gibba L. plants placed in the secondary clarifier and grown in natural water. The amounts of antioxidant vitamins (A, E and C), GSH, GSSG and MDA were determined with HPLC (high performance liquid chromatography) and the amounts of Se were determined fluorimetrically. While significant decrease in amounts of antioxidant vitamins (A, E and C) and Se takes place between the first and the second or third day depending on species and insignificant decrease takes place after that day, the amount of GSH/GSSG ratio decreases until the second day (p < 0.05) and insignificantly increases after that day. Amounts of vitamins (A, E and C), Se and GSH/GSSG ratio for the plants placed in the secondary clarifier are much less than that for control group while an opposite trend was observed in MDA level. The MDA for the plants placed in secondary clarifier has maximum value at the second day, which can be considered as the maximum stress occurring at that day. Consequently, the first two days of treatment time can be taken as acclimation time and after the acclimation time the plant lives in the hostile environmental condition with the certain amount of oxidative stress. As a result, it is determined that wastewater decreases the lifetime of plant by causing metabolic stress on it and affects antioxidant capacity. The lifetime of the plants in the secondary clarifier was determined to be five days since fading toward yellow color (necrosis) in the plants was observed at the fifth day.     

Generalized rate equation for single-substrate enzyme catalyzed reactions

The most widely used rate expression for single-substrate enzyme catalyzed reactions, namely the Michaelis-Menten kinetics is based upon the assumption that enzyme concentration is in excess of the substrate in the medium and the rate is mainly limited by the substrate concentration according to saturation kinetics. However, this is only a special case and the actual rate expression varies depending on the initial enzyme/substrate ratio (E₀/S₀). When the substrate concentration exceeds the enzyme concentration the limitation is due to low enzyme concentration and the rate increases with the enzyme concentration according to saturation kinetics. The maximum rate is obtained when the initial concentrations of the enzyme and the substrate are equal. A generalized rate equation was developed in this study and special cases were discussed for enzyme catalyzed reactions.     

Defining the Far-Red Limit of Photosystem II in Spinach

The far-red limit of photosystem II (PSII) photochemistry was studied in PSII-enriched membranes and PSII core preparations from spinach (Spinacia oleracea) after application of laser flashes between 730 and 820 nm. Light up to 800 nm was found to drive PSII activity in both acceptor side reduction and oxidation of the water-oxidizing CaMn₄ cluster. Far-red illumination induced enhancement of, and slowed down decay kinetics of, variable fluorescence. Both effects reflect reduction of the acceptor side of PSII. The effects on the donor side of PSII were monitored using electron paramagnetic resonance spectroscopy. Signals from the S₂-, S₃-, and S₀-states could be detected after one, two, and three far-red flashes, respectively, indicating that PSII underwent conventional S-state transitions. Full PSII turnover was demonstrated by far-red flash-induced oxygen release, with oxygen appearing on the third flash. In addition, both the pheophytin anion and the Tyr Z radical were formed by far-red flashes. The efficiency of this far-red photochemistry in PSII decreases with increasing wavelength. The upper limit for detectable photochemistry in PSII on a single flash was determined to be 780 nm. In photoaccumulation experiments, photochemistry was detectable up to 800 nm. Implications for the energetics and energy levels of the charge separated states in PSII are discussed in light of the presented results.     

Effects of pH on the S(3) state of the oxygen evolving complex in photosystem II probed by EPR split signal induction

The electrons extracted from the CaMn(4) cluster during water oxidation in photosystem II are transferred to P(680)(+) via the redox-active tyrosine D1-Tyr161 (Y(Z)). Upon Y(Z) oxidation a proton moves in a hydrogen bond toward D1-His190 (His(Z)). The deprotonation and reprotonation mechanism of Y(Z)-OH/Y(Z)-O is of key importance for the catalytic turnover of photosystem II. By light illumination at liquid helium temperatures (～5 K) Y(Z) can be oxidized to its neutral radical, Y(Z)(?). This can be followed by the induction of a split EPR signal from Y(Z)(?) in a magnetic interaction with the CaMn(4) cluster, offering a way to probe for Y(Z) oxidation in active photosystem II. In the S(3) state, light in the near-infrared region induces the split S(3) EPR signal, S(2)'Y(Z)(?). Here we report on the pH dependence for the induction of S(2)'Y(Z)(?) between pH 4.0 and pH 8.7. At acidic pH the split S(3) EPR signal decreases with the apparent pK(a) (pK(app)) ～ 4.1. This can be correlated to a titration event that disrupts the essential H-bond in the Y(Z)-His(Z) motif. At alkaline pH, the split S(3) EPR signal decreases with the pK(app) ～ 7.5. The analysis of this pH dependence is complicated by the presence of an alkaline-induced split EPR signal (pK(app) ～ 8.3) promoted by a change in the redox potential of Y(Z). Our results allow dissection of the proton-coupled electron transfer reactions in the S(3) state and provide further evidence that the radical involved in the split EPR signals is indeed Y(Z)(?).     

Accuracy of Doppler-echocardiographic mean pulmonary artery pressure for diagnosis of pulmonary hypertension

Background

The validity of Doppler echocardiographic (DE) measurement of systolic pulmonary artery pressure (sPAP) has been questioned. Recent studies suggest that mean pulmonary artery pressure (mPAP) might reflect more accurately the invasive pressures.

Methodology/Principal Findings

241 patients were prospectively studied to evaluate the diagnostic accuracy of mPAP for the diagnosis of PH. Right heart catheterization (RHC) and DE were performed in 164 patients mainly for preoperative evaluation of heart valve dysfunction. The correlation between DE and RHC was better when mPAP (r = 0.93) and not sPAP (r = 0.81) was assessed. Bland-Altman analysis revealed a smaller variation of mPAP than sPAP. The following ROC analysis identified that a mPAP≥25.5 mmHg is useful for the diagnosis of PH. This value was validated in an independent cohort of patients (n = 50) with the suspicion of chronic-thromboembolic pulmonary hypertension. The calculated diagnostic accuracy was 98%, based on excellent sensitivity of 98% and specificity of 100%. The corresponding positive and negative predictive values were 100%, respectively 88%.

Conclusion

mPAP has been found to be highly accurate for the initial diagnosis of PH. A cut-off value of 25.5 mmHg might be helpful to avoid unnecessary RHC and select patients in whom RHC might be beneficial.