Mehmet Sayım Karacan

Binuclear manganese (III) complexes as electron donors in D1/D2/cytochrome b559 preparations isolated from spinach photosystem II membrane fragments.

Abstract The capability of different manganese complexes to act as PS II electron donors in D1/D2/ cytochrome b 559 complexes has been analyzed by measuring actinic light-induced absorption changes at 680 nm (650 nm) and 340 nm, reflecting the photoaccumulation of Pheophytin- (Pheo-) and the reduction of NADP+ respectively. The data obtained reveal: a) the donor capacity of synthetic binuclear Mn(III)2 complexes containing aromatic ligands significantly exceeds that for MnCl2 in both cases, i.e. Pheo- photoaccumulation and NADP+ reduction; b) manganese complexes can serve as suitable electron donors for light-induced NADP+ reduction catalyzed by D1/D2/cytochrome b559 complexes and ferredoxin plus ferredoxin- NADP+ reductase under anaerobic conditions and c) the specific turnover rate of the system leading to NADP+ reduction is extremely small. The implications of these findings are briefly discussed.

Quantitative structure-activity relationship analysis of perfluoroiso-propyldinitrobenzene derivatives known as photosystem II electron transfer inhibitors.

Quantitative structure-activity relationship (QSAR) analysis of the twenty-six perfluoroisopropyl-dinitrobenzene (PFIPDNB) derivatives was performed to explain their ability to suppress photochemical activity of the plants photosystem II using chloroplasts and subchloroplast thylakoid membranes enriched in photosystem II, called DT-20. Compounds were optimized by semi-empirical PM3 and DFT/B3LYP/6-31G methods. The Heuristic and the Best Multi-Linear Regression (BMLR) method in CODESSA were used to select the most appropriate molecular descriptors and to develop a linear QSAR model between experimental pI(50) values and the most significant set of the descriptors. The obtained models were validated by cross-validation (R(2)(cv)) and internal validation to confirm the stability and good predictive ability. The obtained eight models with five-parameter show that: (a) coefficient (R(2)) value of the chloroplast samples are slightly higher than that of the DT-20 samples both of Heuristic and BMLR models; (b) the coefficients of the BMLR models are slightly higher than that of Heuristic models both of chloroplasts and DT-20 samples; (c) The YZ shadow parameter and the indicator parameter, for presence of NO(2) substituent in the ring, are the most important descriptor at PM3-based and DFT-based QSAR models, respectively. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Direct determination of selenium in whole blood by anodic stripping voltammetry

Trace quantities of selenium can be determined in the presence of iron, copper and lead using anodic stripping voltammetry, depositing at −0.60 V in 0.1M HClO4 and stripping in the anodic direction. Two separate peaks are observed at −0.25 V and −0.10 V belonging to copper and selenium, respectively. Sometimes one peak may be observed for both copper and selenium. In this case one more stripping (without deposition) must be done to obtain separate peaks. After standard addition, two strippings have to be done also. With this proposed method, 10−7M selenium could be determined as (1.09±0.03) × 10−7M with a 90% confidence interval in blood samples without any separation.

Characterization of nineteen antimony(III) complexes as potent inhibitors of photosystem II, carbonic anhydrase, and glutathione reductase

Nineteen antimony(III) complexes were obtained and examined as possible herbicides. Six of these were synthesized for the first time, and their structures were identified using elemental analyses, 1H-NMR, 13C-NMR, FTIR, LCMS, magnetic susceptibility, and conductivity measurement techniques. For the nineteen examined antimony(III) complexes their most-stable forms were determined by DFT/B3LYP/LanL2DZ calculation method. These compounds were examined for effects on photosynthetic electron transfer and carbonic anhydrase activity of photosystem II, and glutathione reductase from chloroplast as well were investigated. Our results indicated that all antimony(III) complexes inhibited glutathione reductase activity of chloroplast. A number of these also exhibited good inhibitory efficiency of the photosynthetic and carbonic anhydrase activity of Photosystem II.

A new method for screening glutathione reductase inhibitors using square wave voltammetry

A square wave voltammetric method was developed for the detection of glutathione reductase (GR) activity. The method is based upon the direct determination of glutathione (GSH) produced by nicotinamide adenine dinucleotide phosphate (NADPH)-dependent reduction of glutathione disulfide (GSSG). Enzyme activity was represented by an increase in steady-state reduction current of GSH and this current was monitored voltammetrically. At the optimized working condition, reduction potential of GSH was found at −0.44 V with a hanging mercury drop electrode versus an Ag/AgCl electrode. The reduction current was directly proportional to GSH concentration in the range 2.63–800 μM with a lower detection limit of 0.79 μM and lower quantification limit of 2.63 μM. Inhibitory activities of four antimony(III) compounds were determined by this method, and obtained IC50 values were compared with previous data. In addition, an electrochemical study of these compounds showed that their reductions have an EC mechanism; the current is diffusion controlled, and Ep/2 values are proportional to inhibitor activity.

Evaluation of new Cu(II) complexes as a novel class of inhibitors against plant carbonic anhydrase, glutathione reductase and photosynthetic activity in photosystem II

Increasing inefficiency of production of important agricultural plants raises one of the biggest problems in the modern world. Herbicide application is still the best method of weed management. Traditional herbicides blocking only one of the plant metabolic pathways is ineffective due to the rapid growth of herbicide-resistant weeds. The synthesis of novel compounds effectively suppressing several metabolic processes, and therefore achieving the synergism effect would serve as the alternative approach to weed problem. For this reason, recently, we synthesized a series of nine novel Cu(II) complexes and four ligands, characterized them with different analyses techniques, and carried out their primary evaluation as inhibitors of photosynthetic electron transfer in spinach thylakoids (design, synthesis, and evaluation of a series of Cu(II) based metal–organic complexes as possible inhibitors of photosynthesis, J Photochem Photobiol B, submitted). Here, we evaluated in vitro inhibitory potency of these agents against: photochemistry and carbonic anhydrase activity of photosystem II (PSII); α-carbonic anhydrase from bovine erythrocytes; as well as glutathione reductase from chloroplast and baker’s yeast. Our results show that all Cu(II) complexes excellently inhibit glutathione reductase and PSII carbonic anhydrase activity. Some of them also decently inhibit PSII photosynthetic activity.

Reconstitution of the Mn-depleted photosystem 2 by using some manganese complexes

Restoration of electron flow and oxygen-evolution quantity of Mn-depleted photosystem 2 (PS2) was performed with using synthetic manganese complexes Mn(im)6Cl2, Mn(im)2Cl2, Mn(5-Clsalgy)2, and Mn(salgy)2 instead of original manganese cluster for reconstruction of electron transport and oxygen evolution.

Is carbonic anhydrase activity of photosystem II required for its maximum electron transport rate

It is known, that the multi-subunit complex of photosystem II (PSII) and some of its single proteins exhibit carbonic anhydrase activity. Previously, we have shown that PSII depletion of HCO3-/CO2 as well as the suppression of carbonic anhydrase activity of PSII by a known inhibitor of α‑carbonic anhydrases, acetazolamide (AZM), was accompanied by a decrease of electron transport rate on the PSII donor side. It was concluded that carbonic anhydrase activity was required for maximum photosynthetic activity of PSII but it was not excluded that AZM may have two independent mechanisms of action on PSII: specific and nonspecific. To investigate directly the specific influence of carbonic anhydrase inhibition on the photosynthetic activity in PSII we used another known inhibitor of α‑carbonic anhydrase, trifluoromethanesulfonamide (TFMSA), which molecular structure and physicochemical properties are quite different from those of AZM. In this work, we show for the first time that TFMSA inhibits PSII carbonic anhydrase activity and decreases rates of both the photo-induced changes of chlorophyll fluorescence yield and the photosynthetic oxygen evolution. The inhibitory effect of TFMSA on PSII photosynthetic activity was revealed only in the medium depleted of HCO3-/CO2. Addition of exogenous HCO3- or PSII electron donors led to disappearance of the TFMSA inhibitory effect on the electron transport in PSII, indicating that TFMSA inhibition site was located on the PSII donor side. These results show the specificity of TFMSA action on carbonic anhydrase and photosynthetic activities of PSII. In this work, we discuss the necessity of carbonic anhydrase activity for the maximum effectiveness of electron transport on the donor side of PSII.