Evaluation of the role of State transitions in determining the efficiency of light utilisation for CO2 assimilation in leaves

Wheat leaves were exposed to light treatments that excite preferentially Photosystem I (PS I) or Photosystem II (PS II) and induce State 1 or State 2, respectively. Simultaneous measurements of CO₂ assimilation, chlorophyll fluorescence and absorbance at 820 nm were used to estimate the quantum efficiencies of CO₂ assimilation and PS II and PS I photochemistry during State transitions. State transitions were found to be associated with changes in the efficiency with which an absorbed photon is transferred to an open PS II reaction centre, but did not correlate with changes in the quantum efficiencies of PS II photochemistry or CO₂ assimilation. Studies of the phosphorylation status of the light harvesting chlorophyll protein complex associated with PS II (LHC II) in wheat leaves and using chlorina mutants of barley which are deficient in this complex demonstrate that the changes in the effective antennae size of Photosystem II occurring during State transitions require LHC II and correlate with the phosphorylation status of LHC II. However, such correlations were not found in maize leaves. It is concluded that State transitions in C₃ leaves are associated with phosphorylation-induced modifications of the PS II antennae, but these changes do not serve to optimise the use of light absorbed by the leaf for CO₂ assimilation.Abbreviations Fm, Fo, Fv maximal, minimal and variable fluorescence yields - Fm, Fv maximal and variable fluorescence yields in a light adapted state - LHC II light harvesting chlorophyll a/b protein complex associated with PS II - q_P photochemical quenching - A₈₂₀ light-induced absorbance change at 820 nm - _{PS I}, _{PS II} relative quantum efficiencies of PS I and PS II photochemistry - _{CO 2} quantum yield of CO₂ assimilation     

Evolutionary study of multigenic families mapping close to the human MHC class I region

Summary During a search for novel coding sequences within the human MHC class I region (chromosome 6p21.3), we found an exon (named B30-2) coding for a 166-amino-acid peptide which is very similar to the C-terminal domain of several coding sequences: human 52-kD Sjögren's syndrome nuclear antigen A/Ro (SS-A/Ro) and ret finger protein (RFP), Xenopus nuclear factor 7 (XNF7), and bovine butyrophilin. The first three of these proteins share similarities over the whole length of the molecule whereas butyrophilin is similar in the C-terminal domain. The N-terminal domain of butyrophilin is similar to rat myelin/oligodendrocyte glycoprotein (MOG) and chicken B blood group system (B-G) protein. These domains are components of a new subfamily of the immunoglobulin superfamily (IgSF). Butyrophilin is thus a mosaic protein composed of the MOG/B-G Ig-like domain and the C-terminal domain of 52-kD SS-A/Ro, RFP, and XNF7 (1330-2-like domain). Moreover, in situ hybridization shows that RFP, butyrophilin, and MOG map to the human chromosome 6p2l.3-6p22 region and are thus close to the MHC class I genes. It is therefore possible that the butyrophilin gene is the product of an exon shuffling event which occurred between ancestors of the RFP and MOG genes. To our knowledge, this is the first example of the colocalization of a chimeric gene and its putative progenitors. Finally, regulatory protein T-lymphocyte 1 (Rpt-1) shares similarities with the N-terminal halves of RFP, 52-kD SS-A/Ro, and XNF7, but not with the B30-2-like domain. We show that the ancestral Rpt-l gene evolved by overprinting. Correspondence to: P. Pontarotti     

Formation of acetyl-CoA in Zymomonas mobilis by a pyruvate dehydrogenase complex

In the gram negative, obligately ethanologenic bacterium Zymomonas mobilis a pyruvate dehydrogenase complex was identified and the complex was enriched from cell extracts. This multienzyme complex is responsible for acetyl-CoA biosynthesis from pyruvate. No activities of related multienzyme complexes, 2-ketoglutarate dehydrogenase and branched chain keto acid dehydrogenase, could be detected.     

Novel palladium(II) and Zinc(II) Schiff base complexes: Synthesis,biophysical studies,and anticancer activity investigation

BackgroundSchiff base metal complexes are considered promising chemotherapeutic agents due to their potential application in cancer therapy.MethodsThe current work sought to synthesize a brand-new Schiff base ligand obtained from 2-hydroxybenzohydrazide and (E)− 1-(2-(p-tolyl)hydrazono)propan-2-one with metal ions which included Pd(II) and Zn(II) ions. Elemental analyses, FT-IR, mass spectra, 1H NMR, UV-Vis spectrometer, and computational analysis characterized the compound's structure. In vitro, the breast cancer cell line (MCF-7) was tested for its sensitivity to Schiff base (HL) and its Pd(II) and Zn(II) complexes. The half-maximal inhibitory concentration IC₅₀ of the compounds was determined and used to perform the comet assay, which was carried out to reveal the photo-induced DNA damaging ability of the compounds of individual cells. Moreover, the compounds' effects on antioxidant defense systems of enzymes in cells: superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities and oxidant Malondialdehyde (MDA) were examined in MCF-7 cells.ResultsThe Pd(II) complex displayed approximately the same IC₅₀ as Cisplatin, while Zn(II) complex had better activity than Cisplatin with very low IC₅₀, 1.40 μg/ml. Significant alterations in SOD, CAT, GPx, and MDA production were discovered, inducing oxidative stress, enlarging ROS production, and reducing the antioxidant amount. This change was approximately similar in most compounds. Consequently, it promoted apoptosis, particularly the Zn(II) complex, which demonstrated an improved impact because of its ability to influence the antioxidant defense systems of enzymes, mostly SOD and GPx, besides increasing MDA levels.ConclusionIt can be concluded that Zn(II) complex is the most effective anticancer drug since it induced a very similar genotoxic effect as Cisplatin and has a very low IC₅₀ value.     

LIGHT-HARVESTING PIGMENT-PROTEIN COMPLEXES OF THE ULVOPHYCEAE (CHLOROPHYTA):CHARACTERIZATION AND PHYLOGENETIC SIGNIFICANCE1

Photosystem II light-harvesting complexes were isolated from a number of ulvophycean algae. Some of these light-harvesting complexes displayed unusual features, most notably a high apparent molecular weight (ca. 58,000) when isolated by lithium doderyl sulfate polyarrylamide gel electrophoresis. Other ulvophycean light-harvesting complexes had a low-molecular weight (ca. 30,000). The distribution of the high-molecular weight complex was limited to certain members of the Caulerpales and Blastophysa rhizopus (Siphanocladales). Within the Caulerpales, there were also spectral differences between the high-molecular weight and low-molecular weight light-harvesting complex types. The differences in light-harvesting complexes in the Ulvophyceae suggest that there are two lines of evolution in the Caulerpales and that Blastophysa may be an intermediate between the Siphon-ocladales and the Caulerpales.     

The cellular pathway of sucrose transport in developing cotyledons ofVicia faba L. andPhaseolus vulgaris L.: a physiological assessment

The cellular pathway of sugar uptake in developing cotyledons of Vicia faba L. and Phaseolus vulgaris L. seed was evaluated using a physiological approach. The cotyledon interface with the seed coat is characterised by a specialised dermal cell complex. In the case of Vicia faba cotyledons, the epidermal component of the dermal cell complex is composed of transfer cells. Sucrose is the major sugar presented to the outer surface of both cotyledons and it is taken up from the apoplasm unaltered. Estimated sucrose concentrations within the apparent free space of Vicia and Phaseolus cotyledons were 105 and 113 mM respectively. Rates of in-vitro uptake of [¹⁴C]sucrose by cotyledon segments or by whole cotyledons following physical removal or porter inactivation of the outer cells demonstrated that, for both Vicia and Phaseolus cotyledons, the dermal cell complexes are the most intense sites of sucrose uptake. Accumulation of [¹⁴C]sucrose in the storage parenchyma of whole cotyledons was directly affected by experimental manipulation of uptake by the outer cell layers and plasmolytic disruption of the interconnecting plasmodesmata. These findings indicated that sucrose accumulated by the dermal cell complexes is transported symplasmically to the storage parenchyma. Overall, it is concluded that the dermal cell complexes of the developing legume embryo, irrespective of the presence or absence of wall ingrowths, are the major sites for the uptake of sucrose released from the maternal tissues to the seed apoplasm. Thereafter, the accumulated sucrose is transported radially inward through the symplast to the storage parenchyma.Abbreviations AFS apparent free space - CF 5-(6)-carboxyfluorescein - CFDA 5-(6)-carboxyfluorescein diacetate - Mes 2-(N-morpholino)ethanesulfonic acid - PCMBS p-chloromercuribenzenesulfonic acid - SRG sulphorhodamine G The investigation was supported by funds from the Research Management Committee, The University of Newcastle and the Australian Research Council. One of us, R. McDonald, gratefully acknowledges the support of an Australian Postgraduate Research Award. We are grateful to Stella Savoury for preparing the photomicrographs.     

Novel findings on the copper catalysed oxidation of cysteine

Summary The oxidation of cysteine (RSH) has been studied by using O₂, ferricytochrome c (Cyt c) and nitro blue tetrazolium (NBT) as electron acceptors. The addition of 200M Cu^II to a solution of 2mM cysteine, pH 7.4, produces an absorbance with a peak at 260 nm and a shoulder at 300 nm. Generation of a cuprous bis-cysteine complex (RS-Cu^I-SR) is responsible for this absorbance. In the absence of O₂ the absorbance is stable for long time while in the presence of air it vanishes slowly only when the cysteine excess is consumed. The neocuproine assay and the EPR analysis show that the metal remains reduced in the course of the oxidation of cysteine returning to the oxidised form at the end of reaction when all RSH has been oxidised to RSSR. Addition of Cu^II enhances the reduction rate of Cyt c and of NBT by cysteine also under anaerobiosis indicating the occurrence of a direct reduction of the acceptor by the complex. It is concluded that the cuprous bis-cysteine complex (RS-Cu^I-SR) is the catalytic species involved in the oxidation of cysteine. The novel finding of the stability of the complex together with the metal remaining in the reduced form during the oxidation suggest sulfur as the electron donor in the place of the metal ion.Abbreviations RSH cysteine - RS^– cysteine in the thiolate form - RS^· thiyl radical of cysteine - RSSR cystine - Cyt c cytochrome c - SOD superoxide dismutase - NBT nitro blue tetrazolium - NBF nitro blue formazan - DTNB 5,5-dithiobis-2-nitrobenzoic acid - DTPA diethylenetriaminepentaacetic acid Dedicated to prof. A. Ballio ob the occasion of his 75th birthday.     

Multiple molecular recognition properties of the lipocalin protein family

The lipocalins, a diverse family of small extracellular ligand proteins, display a remarkable range of different molecular properties. While their binding of small hydrophobic molecules, and to a lesser extent their binding to cell surface receptors, is well known, it is shown here that formation of macromolecular complexes is also a common feature of this family. Analysis of known crystallographic structures reveals that the lipocalins process a conserved common structure: an antiparallel β-barrel with a repeated +1 topology. Comparisons show that within this overall similarity the structure of individual proteins is specifically adapted to bind their particular ligands, forming a binding site from an internal cavity (within the barrel) and/or an external loop scaffold, which gives rise to different binding modes that reflects the need to accommodate ligands of different shape, size, and chemical structure. The architecture of the lipocalin fold suggests that the both the ends and sides of this barrel are topologically distinct, differences also apparent in analyses of structural and sequence variation within the family. These different can be linked to experimental evidence suggesting a possible functional dichotomy between the two ends of the lipocalin fold. The structurally invariant end of the molecule may be implicated in general binding small ligands and forming macromolecular complexes via an exposed binding surface.     

Superoxide dismutase mimetic activity of a cyclic tetrameric Schiff base N-coordinated Cu(II) complex

A pulse radiolytic study using the cyclic tetrameric Schiff base N-coordinated copper complex Cu(TAAB)²⁺ has been performed. The reaction of the Cu(TAAB)²⁺ complex with superoxide revealed pseudo first-order characteristics with the rate constant of k ₂ = (2.9 ± 0.5) × 10⁸ mol^–1 s^–1 dm³. The complex survive presence of competing serum albumin in physiological concentrations. The complex stability constant K = 1.15 × 10¹⁸ (log K = 18.06) is two orders of magnitude higher than that of Cu(II)-serum albumin (log K = 16.2). Transient changes of the stability during the oxidation/reduction process and in the presence of 600 /mol l^–1 albumin did not affect significantly either the electronic absorption of the complex or its catalytic activity.