Energy metabolism in the cyanobacterium Plectonema boryanum. Participation of the thylakoid photosynthetic electron transfer chain in the dark respiration of NADPH and NADH

The oxidation of NADPH and NADH was studied in the light and in the dark using sonically derived membrane vesicles and osmotically shocked spheroplasts. These two types of cell-free membrane preparations mostly differ in that the cell and thylakoid membranes are scrambled in the former type and that they are more or less separated in the latter type of preparations. In the light, using both kinds of preparations, each of NADPH and NADH donates electrons via the plastoquinone-cytochrome $\text{b}\text{c}$ redox complex (Qbc redox complex) to the thylakoid membrane-bound cytochrome c-553 preoxidized by a light flash and to methylviologen via Photosystem I. NADPH donates electrons to the thylakoid membrane via a weakly rotenone-sensitive dehydrogenase to a site that is situated beyond the 3(3′,4′-dichlorophenyl)-1,1-dimethylurea sensitive site and before plastoquinone. Ferredoxin and easily soluble cytoplasmic proteins are presumably not involved in light-mediated NADPH oxidation. Inhibitors of electron transfer at the Qbc redox complex as the dinitrophenylether of 2-iodo-4-nitrothymol, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone and 2-n-heptyl-4-hydroxy-quinone-N-oxide are effective, but antimycin A and KCN are not. The oxidation of NADH showed comparable sensitivity to these inhibitors. However, the oxidation of NADH is antimycin-A-sensitive regardless of the kind of membrane preparation used, indicating that in this case electrons are donated to a different site on the thylakoid membrane. In the dark, NADPH and NADH donate electrons at sites that behave similar to those of light-mediated oxidation, indicating that the initial steps of electron transfer are situated at the thylakoid membranes. However, NADPH oxidation is in some cases not sensitive to inhibitors active at the Qbc redox complex. It is concluded that O₂ reduction takes place at two different sites, one partly developed in vitro, situated near the rotenone-sensitive NADPH dehydrogenase, and another, highly KCN-sensitive one, situated beyond the Qbc redox complex and used in vivo. The terminal oxygen-reducing step of NADPH and NADH oxidation in the dark showed a preparation-dependent sensitivity for KCN, more than 80% inhibition in sonically derived membrane vesicles and less than 30% inhibition in osmotically shocked spheroplasts. From this result we tentatively conclude that the highly KCN-sensitive oxidase is not necessarily located at the thylakoid membrane and could be located at the cytoplasmic membrane.     

Evolution of 1, 3, 5-trisubstituted bipyrazole scaffold based platinum(II) complexes as a biological active agent

Abstract

Square planar mononuclear platinum(II) complexes having general formula [Pt(Lⁿ)Cl₂], (where, Lⁿ?=?L^1–4) were synthesized with neutral bidentate heterocyclic 1,3,5-trisubstituted bipyrazole based ligands. The synthesized compounds were characterized by physicochemical method such as TGA, molar conductance, micro-elemental analysis and magnetic moment, and spectroscopic method such as, FT-IR, UV–vis, ¹H NMR, ¹³C NMR and mass spectrometry. Biological applications of the compounds were carried out using in vitro brine shrimp lethality bioassay, in vitro antimicrobial study against five different pathogens, and cellular level cytotoxicity against Schizosaccharomyces pombe (S. Pombe) cells. Pt(II) complexes were tested for DNA interaction activities using electronic absorption titration, viscosity measurements study, fluorescence quenching technique and molecular docking assay. Binding constants (K_b) of ligands and complexes were observed in the range of 0.23–1.07?×?10⁵?M^?1 and 0.51–3.13?×?10⁵?M^?1, respectively. Pt(II) complexes (I–IV) display an excellent binding tendency to biomolecule (DNA) and possess comparatively high binding constant (K_b) values than the ligands. The DNA binding study indicate partial intercalative mode of binding in complex-DNA. The gel electrophoresis activity was carried out to examine DNA nuclease property of pUC19 plasmid DNA.     

Identification and characterization of the mitochondrial membrane sorting signals in phosphatidylserine decarboxylase 1 from Saccharomyces cerevisiae

Phosphatidylserine decarboxylase 1 (Psd1p) catalyzes the formation of the majority of phosphatidylethanolamine (PE) in the yeast Saccharomyces cerevisiae. Psd1p is localized to mitochondria, anchored to the inner mitochondrial membrane (IMM) through membrane spanning domains and oriented towards the mitochondrial intermembrane space. We found that Psd1p harbors at least two inner membrane-associated domains, which we named IM1 and IM2. IM1 is important for proper orientation of Psd1p within the IMM (Horvath et al., J. Biol. Chem. 287 (2012) 36744–55), whereas it remained unclear whether IM2 is important for membrane-association of Psd1p. To discover the role of IM2 in Psd1p import, processing and assembly into the mitochondria, we constructed Psd1p variants with deletions in IM2. Removal of the complete IM2 led to an altered topology of the protein with the soluble domain exposed to the matrix and to decreased enzyme activity. Psd1p variants lacking portions of the N-terminal moiety of IM2 were inserted into IMM with an altered topology. Psd1p variants with deletions of C-terminal portions of IM2 accumulated at the outer mitochondrial membrane and lost their enzyme activity. In conclusion we showed that IM2 is essential for full enzymatic activity, maturation and correct integration of yeast Psd1p into the inner mitochondrial membrane.     

Flexible coupling between light-dependent electron and vectorial proton transport in illuminated leaves of C3 plants. Role of photosystem I-dependent proton pumping

The role of cyclic electron transport has been re-examined in leaves of C₃ plants because the bioenergetics of chloroplasts (H⁺/e = 3 in the presence of a Q-cycle; H⁺/ATP = 4 of ATP synthesis) had suggested that cyclic electron flow has no function in C₃ photosynthesis. After light activation of pea leaves, the dark reduction of P700 (the donor pigment of PSI) following far-red oxidation was much accelerated. This corresponded to loss of sensitivity of P700 to oxidation by far-red light and a large increase in the number of electrons available to reduce P700⁺ in the dark. At low CO₂ and O₂ molar ratios, far-red light was capable of decreasing the activity of photosystem II (measured as the ratio of variable to maximal chlorophyll fluorescence, F_v/F_m) and of increasing light scattering at 535 nm and zeaxanthin synthesis, indicating formation of a transthylakoid pH gradient. Both the light-induced increase in the number of electrons capable of reducing far-red-oxidised P700 and the decline in F_v/F_m brought about by far-red in leaves were prevented by methyl viologen. Antimycin A inhibited CO₂-dependent O₂ evolution of pea leaves at saturating but not under limiting light; in its presence, far-red light failed to decrease F_v/F_m. The results indicate that cyclic electron flow regulates the quantum yield of photosystem II by decreasing the intrathylakoid pH when there is a reduction in the availability of electron acceptors at the PSI level (e.g. during drought or cold stresses). It also provides ATP for the carbon-reduction cycle under high light. Under these conditions, the Q-cycle is not able to maintain a H⁺/e ratio of 3 for ATP synthesis: we suggest that the ratio is flexible, not obligatory. Received: 23 February 1999 / Accepted: 19 August 1999     

The physical basis of reflective communication between fish,with special reference to the horse mackerel,Trachurus trachurus

Some properties of reflecting structures in the external surfaces of Trachurus trachurus and some other fish are described. These are related to the hypothesis that such structures are useful, especially to schooling fish, for communicating information on relative positions, orientations, and movements between neighbours. In addition to the silvery layers on the main body surfaces, there are: (a) highly silvered patches on the tail, the pectoral fins and the jaws which, in the sea, will become much brighter or darker with any movement such as a tailbeat or mouth opening which changes their orientations in the ambient lightfield, and (b) structures such as the dorsal lateral line which, in the sea, will only appear bright from certain directions. To us, the colours of the ventral flanks change from bright red to blue with direction orientations and have special reflectivity curves close to those predicted by A.F. Huxley for interference reflectors which are ''ideal'' λ/4 stacks of guanine crystals and cytoplasm. The wavebands best reflected by such platelets move to shorter wavelengths with increasing angle of incidence, also in accord with these equations. At normal incidence, the outer layer of platelets reflects maximally for far-red light which penetrates only a short distance in the sea. Such layers can, however, be useful at oblique angles where they reflect maximally in the yellow and blue. The inner layer of reflectors reflects very strongly in the blue at normal incidence, but reflects in the ultra-violet at oblique angles. Some theoretical studies are made on the ways in which the patterns of reflectivity by single and superposed layers of λ/4 stacks could signal a fish''s movements or its position relative to its neighbours.     

Improving diagnostic strategies for ovarian cancer in Filipino women using ultrasound imaging and a multivariate index assay

ObjectiveTo evaluate the clinical performance and overall utility of imaging and biomarker assays in discriminating between benign and malignant ovarian masses in a Filipino population.MethodsThis is a prospective cohort study among Filipino women undergoing assessment for an ovarian mass in a tertiary center. All included patients underwent a physical examination before level III specialist ultrasonographic and Doppler evaluation, multivariate index assay (MIA2G), and surgery for an adnexal mass. Ovarian tumors were classified as high-risk for malignancy based on the International Ovarian Tumour Analysis (IOTA) – Logistic Regression 2 (LR2) score. The ovarian imaging and biomarker results were correlated with the reference standard: histological findings.ResultsAmong the 379 women with adnexal masses enrolled in this study, 291 were evaluable with ultrasound imaging, biomarker assays, and histopathological results. The risk of malignancy was higher for women classified as high-risk based on IOTA-LR2 (≥10%). The sensitivity, specificity, and diagnostic accuracy for the prediction of malignancy were 81.2%, 81%, and 0.81 (95% CI: 0.77–0.86) for IOTA-LR2; 77.5%, 66.7%, and 0.72 (95% CI: 0.67–0.77) for CA-125; and 91.3%, 41.2%, and 0.66 (95% CI: 0.62–0.71) for MIA2G. A combination of IOTA-LR2 and MIA2G significantly influenced the diagnostic performance and the result. When MIA2G was combined with IOTA-LR2 in parallel, the sensitivity (94.2%) and NPV (87.7%) increased, but the specificity (37.3%) decreased. When combined with IOTA-LR2 in series, there were fewer false positives, which resulted in improved specificity (85%).ConclusionThis study determined the utility of ovarian imaging and a second-generation multivariate index assay in predicting the risk of ovarian malignancy. IOTA-LR2 and MIA2G were useful in classifying patients with a high risk for ovarian malignancy.