Probing subtle coordination changes in the iron-quinone complex of photosystem II during charge separation,by the use of NO

The terminal electron acceptor of Photosystem II, PSII, is a linear complex consisting of a primary quinone, a non-heme iron(II), and a secondary quinone, Q(A)Fe(2+)Q(B). The complex is a sensitive site of PSII, where electron transfer is modulated by environmental factors and notably by bicarbonate. Earlier studies showed that NO and other small molecules (CN(-), F(-), carboxylate anions) bind reversibly on the non-heme iron in competition with bicarbonate. In the present study, we report on an unusual new mode of transient binding of NO, which is favored in the light-reduced state (Q(A)(-)Fe(2+)Q(B)) of the complex. The related observations are summarized as follows: (i) Incubation with NO at -30 degrees C, following light-induced charge separation, results in the evolution of a new EPR signal at g = 2.016. The signal correlates with the reduced state Q(A)(-)Fe(2+) of the iron-quinone complex. (ii) Cyanide, at low concentrations, converts the signal to a more rhombic form with g values at 2.027 (peak) and 1.976 (valley), while at high concentrations it inhibits formation of the signals. (iii) Electron spin-echo envelope modulation (ESEEM) experiments show the existence of two protein (14)N nuclei coupled to electron spin. These two nitrogens have been detected consistently in the environment of the semiquinone Q(A)(-) in a number of PSII preparations. (iv) NO does not directly contribute to the signals, as indicated by the absence of a detectable isotopic effect ((15)NO vs (14)NO) in cw EPR. (v) A third signal with g values (2.05, 2.03, 2.01) identical to those of an Fe(NO)(2)(imidazole) synthetic complex develops slowly in the dark, or faster following illumination. (vi) In comparison with the untreated Q(A)(-)Fe(2+) complex, the present signals not only are confined to a narrow spectral region but also saturate at low microwave power. At 11 K the g = 2.016 signal saturates with a P(1/2) of 110 microW and the g = 2.027/1.976 signal with a P(1/2) of 10 microW. (vii) The spectral shape and spin concentration of these signals is successfully reproduced, assuming a weak magnetic interaction (J values in the range 0.025-0.05 cm(-)(1)) between an iron-NO complex with total spin of (1)/(2) and the spin, (1)/(2), of the semiquinone, Q(A)(-). The different modes of binding of NO to the non-heme iron are examined in the context of a molecular model. An important aspect of the model is a trans influence of Q(A) reduction on the bicarbonate ligation to the iron, transmitted via H-bonding of Q(A) with an imidazole ligand to the iron.     

Biosynthesis of the sesquiterpene germacrene D in Solidago canadensis: 13C and (2)H labeling studies

The biogenetic origin of the isoprenoid building blocks of the sesquiterpene germacrene D was studied in Solidago canadensis. Feeding experiments were carried out with 1-[5,5-D(2)]deoxy-D-xylulose-5-phosphate (D(2)-DOXP), [5-13C]mevalonolactone (13C-MVL) and [1-13C]-D-glucose. The hydrodistillate of a cut shoot fed with D(2)-DOXP was investigated by enantio-MDGC-MS and the volatile fraction of a shoot supplied with 13C-MVL was examined by GC-C-IRMS. The incorporation of [1-13C]-D-glucose was analyzed by quantitative 13C NMR spectroscopy after isolation of germacrene D from the essential oil. Our labeling studies revealed that the biosynthesis of the C-15 skeleton of sesquiterpene germacrene D in Solidago canadensis proceeds predominantly via the methylerythritol phosphate pathway.     

Cloning, chromosomal organization and expression analysis of Neurl, the mouse homolog of Drosophila melanogaster neuralized gene

The Drosophila neuralized (neur) gene belongs to the neurogenic group of genes involved in regulating cell-cell interactions required for neural precursor development. neur mutant phenotypes include strong overcommitment to neural fates at the expense of epidermal fates. The human neuralized homolog (NEURL) has been recently determined and found to map to chromosome 10q25.1 within the region frequently deleted in malignant astrocytomas. Because of its potential importance in developmental processes, we analyzed the structure of the mouse homolog, Neurl, and its expression pattern in embryonic tissues. Neurl activity is detected from early developmental stages in several tissues and organs including neural tissues, limbs, the skeletal system, sense organs and internal organs undergoing epithelial-mesenchymal interactions. Neurl encodes a polypeptide associated with the plasma membrane but also detected in the cytoplasm. Similarly to the Drosophila gene, mammalian neuralized may code for an important regulatory factor.     

Analysis of IL-12 p40 subunit gene and IFN-γ G5644A polymorphisms in Idiopathic Pulmonary Fibrosis

Background

Genes encoding cytokine mediators are prime candidates for genetic analysis in conditions with T-helper (Th) cell disease driven imbalance. Idiopathic Pulmonary Fibrosis (IPF) is a predominantly Th2 mediated disease associated with a paucity of interferon-gamma (IFN-γ). The paucity of IFN-γ may favor the development of progressive fibrosis in IPF. Interleukin-12 (IL-12) plays a key role in inducing IFN-γ production. The aim of the current study was to assess whether the 1188 (A/C) 3'UTR single nucleotide polymorphism (SNP) in the IL-12 p40 subunit gene which was recently found to be functional and the 5644 (G/A) 3' UTR SNP of the IFN-γ gene were associated with susceptibility to IPF.

Methods

We investigated the allelic distribution in these loci in UK white Caucasoid subjects comprising 73 patients with IPF and 157 healthy controls. The SNPs were determined using the polymerase chain reaction in association with sequence-specific primers incorporating mismatches at the 3'-end.

Results

Our results showed that these polymorphisms were distributed similarly in the IPF and control groups

Conclusion

We conclude that these two potentially important candidate gene single nucleotide polymorphisms are not associated with susceptibility to IPF.     

Genetic associations: false or true?

Genetic association studies for multigenetic diseases are like fishing for the truth in a sea of trillions of candidate analyses. Red herrings are unavoidably common, and bias might cause serious misconceptions. However, a sizeable proportion of identified genetic associations are probably true. Meta-analysis, a rigorous, comprehensive, quantitative synthesis of all the available data, might help us to separate the true from the false.     

Thyroid hormone and cardioprotection: Study of p38 MAPK and JNKs during ischaemia and at reperfusion in isolated rat heart

It has been recently shown that long-term thyroxine administration increases the tolerance of the heart to ischaemia. The present study investigated whether thyroxine induced cardioprotection involves alterations in the pattern of p38 mitogen activated protein kinase (p38MAPK) and c-Jun NH₂-terminal kinases (JNKs) activation during ischaemia-reperfusion. L-thyroxine (T4) was administered in Wistar rats (25 g/100 g/day, subcutaneously) for 2 weeks (THYR), while normal animals served as controls (NORM). NORM and THYR isolated rat hearts were perfused in Langendorff mode and subjected to 10 or 20 min of zero-flow global ischaemia only and also to 20 min of ischaemia followed by 10, 20 or 45 min of reperfusion. Postischaemic recovery of left ventricular developed pressure at 45 min of reperfusion was expressed as % of the initial value. Activation of p38 MAPK and JNKs was assessed at the different times of the experimental setting by standard Western blotting techniques using a dual phospho p38MAPK and phospho JNKs (p46/p54) antibodies. Activation of p38 MAPK was significantly attenuated during ischaemia and reperfusion in thyroxine treated hearts compared to normal hearts. JNKs were found to be activated only during the reperfusion period. The levels of phospho JNKs were found to be lower in thyroxine treated hearts as compared to untreated hearts, though not at a statistically significant level. Postischaemic functional recovery was higher in THYR as compared to NORM, p < 0.05. In summary, in hearts pretreated with thyroxine, p38 MAPK was attenuated during ischaemia and at reperfusion and this was associated with improved postischaemic recovery of function.     

One Step forward: Benthic Pelagic Coupling and Indicators for Environmental Status

A large data set from the Eastern Mediterranean was analyzed to explore the relationship between seawater column variables and benthic community status. Our results showed a strong quantitative link between the seawater column variables (Chlorophyll a and Eutrophication Index) and various indicators describing benthic diversity and community composition. The percentage of benthic opportunistic species increased significantly in the stations with high trophic status of the seawater column and so did the strength of the coupling between values of seawater column and benthic indicators. The Eutrophication Index threshold level of 0.85, separating the “Bad and Poor” from “Moderate to High” conditions could serve as an acceptable critical value above which there is a readily observable change in benthic community composition.