Redox and Chemical Activities of the Hemes in the Sulfur Oxidation Pathway Enzyme SoxAX

SoxAX enzymes couple disulfide bond formation to the reduction of cytochrome c in the first step of the phylogenetically widespread Sox microbial sulfur oxidation pathway. Rhodovulum sulfidophilum SoxAX contains three hemes. An electrochemical cell compatible with magnetic circular dichroism at near infrared wavelengths has been developed to resolve redox and chemical properties of the SoxAX hemes. In combination with potentiometric titrations monitored by electronic absorbance and EPR, this method defines midpoint potentials (E_m) at pH 7.0 of approximately +210, −340, and −400 mV for the His/Met, His/Cys⁻, and active site His/CysS⁻-ligated heme, respectively. Exposing SoxAX to S₂O₄²⁻, a substrate analog with E_m ∼−450 mV, but not Eu(II) complexed with diethylene triamine pentaacetic acid (E_m ∼−1140 mV), allows cyanide to displace the cysteine persulfide (CysS⁻) ligand to the active site heme. This provides the first evidence for the dissociation of CysS⁻ that has been proposed as a key event in SoxAX catalysis.     

Microalgal fatty acid composition: implications for biodiesel quality

The fuel properties of microalgal biodiesel are predicted using published microalgal fatty acid (FA) compositions and predictive fuel models. Biodiesels produced from the microalgae investigated are predicted to have extremely poor oxidative stabilities and the majority also have poor cold-flow properties. The cetane number in most cases is out of specification, but less so than the oxidative stability and cold flow. These findings support the idea that feedstocks rich in monounsaturated fatty acids (MUFAs) are desirable for biodiesel but the composition of the saturated fatty acids (SFAs) is also shown to be of great importance. There is an apparent relationship between algal class and the percentage of FAs represented by MUFA. This potentially allows for the identification of high-MUFA algal classes, or at least provides some basis for researchers to make initial selections of target classes for bioprospecting. Comparisons of FA groups between algal classes also show that the SFAs of Mediophyceae contain significantly higher proportions of C14:0, which is in contrast to the normally abundant C16:0 and the Mediophyceae therefore have better cold-flow characteristics than other classes with similar total SFA contents. Certain particularly promising cases for biodiesel production are presented as species level examples of feedstocks that are close to satisfying the biodiesel standards and to further illustrate the challenges that remain. Variation in FA composition as a response to changes in certain environmental variables forms another important facet to feedstock selection and is briefly considered, with suggestions for further research.     

Length and amino acid sequence of peptides substituted for the 5-HT3A receptor M3M4 loop may affect channel expression and desensitization

5-HT3A receptors are pentameric neurotransmitter-gated ion channels in the Cys-loop receptor family. Each subunit contains an extracellular domain, four transmembrane segments (M1, M2, M3, M4) and a 115 residue intracellular loop between M3 and M4. In contrast, the M3M4 loop in prokaryotic homologues is <15 residues. To investigate the limits of M3M4 loop length and composition on channel function we replaced the 5-HT3A M3M4 loop with two to seven alanine residues (5-HT3A-A(n = 2-7)). Mutants were expressed in Xenopus laevis oocytes and characterized using two electrode voltage clamp recording. All mutants were functional. The 5-HT EC(50)'s were at most 5-fold greater than wild-type (WT). The desensitization rate differed significantly among the mutants. Desensitization rates for 5-HT3A-A(2), 5-HT3A-A(4), 5-HT3A-A(6), and 5-HT3A-A(7) were similar to WT. In contrast, 5-HT3A-A(3) and 5-HT3A-A(5) had desensitization rates at least an order of magnitude faster than WT. The one Ala loop construct, 5-HT3A-A(1), entered a non-functional state from which it did not recover after the first 5-HT application. These results suggest that the large M3M4 loop of eukaryotic Cys-loop channels is not required for receptor assembly or function. However, loop length and amino acid composition can effect channel expression and desensitization. We infer that the cytoplasmic ends of the M3 and M4 segments may undergo conformational changes during channel gating and desensitization and/or the loop may influence the position and mobility of these segments as they undergo gating-induced conformational changes. Altering structure or conformational mobility of the cytoplasmic ends of M3 and M4 may be the basis by which phosphorylation or protein binding to the cytoplasmic loop alters channel function.     

Weather indices for designing micro-insurance products for small-holder farmers in the tropics

Agriculture is inherently risky. Drought is a particularly troublesome hazard that has a documented adverse impact on agricultural development. A long history of decision-support tools have been developed to try and help farmers or policy makers manage risk. We offer site-specific drought insurance methodology as a significant addition to this process. Drought insurance works by encapsulating the best available scientific estimate of drought probability and severity at a site within a single number- the insurance premium, which is offered by insurers to insurable parties in a transparent risk-sharing agreement. The proposed method is demonstrated in a case study for dry beans in Nicaragua.     

Biohydrogen production by <Emphasis Type="Italic">Enterobacter cloacae</Emphasis> and <Emphasis Type="Italic">Citrobacter freundii</Emphasis> in carrier induced granules

Carrier induced granular particles comprising Enterobacter cloacae and Citrobacter freundii were used to generate H₂ from sucrose in an anaerobic fluidized bed bioreactor. At a hydraulic retention time of 4.5 h, 95.8% of the sucrose was consumed and the rate of H₂ production reached 180 mmol H₂ l h⁻¹. Biogas composition for H₂ and CO₂ was 42 and 55%, respectively. Alex von Holy—Deceased     

Novel fluorinated acridone derivatives. Part 1: synthesis and evaluation as potential anticancer agents

We report on the synthesis of a novel series of fluorinated acridones from 5-trifluoromethyl-1,3-cyclohexanedione. The cytotoxic activities of the compounds were studied in several cancer cells. Compounds 9a, 9c, 9e, 9f, and 9h exhibited significant anticancer activities in selected cell lines. Compound 9c is the most active showing GI₅₀ that ranged in values from 0.13 to 26 μM, covering a wide range of cancer cell lines.     

Longitudinal Evaluation of the Structure of Replicating and Circulating Hepatitis C Virus Quasispecies in Nonprogressive Chronic Hepatitis C Patients

In previous cross-sectional studies, we demonstrated that, in most patients with chronic hepatitis C, the composition and complexity of the circulating hepatitis C virus (HCV) population do not coincide with those of the virus replicating in the liver. In the subgroup of patients with similar complexities in both compartments, the ratio of quasispecies complexity in the liver to that in serum (liver/serum complexity ratio) of paired samples correlated with disease stage. In the present study we investigated the dynamic behavior of viral population parameters in consecutive paired liver and serum samples, obtained 3 to 6 years apart, from four chronic hepatitis C patients with persistently normal transaminases and stable liver histology. We sequenced 359 clones of a genomic fragment encompassing the E2(p7)-NS2 junction, in two consecutive liver-serum sample pairs from the four patients and in four intermediate serum samples from one of the patients. The results show that the liver/serum complexity ratio is not stable but rather fluctuates widely over time. Hence, the liver/serum complexity ratio does not identify a particular group of patients but a particular state of the infecting quasispecies. Phylogenetic analysis and signature mutation patterns showed that virtually all circulating sequences originated from sequences present in the liver specimens. The overall behavior of the circulating viral quasispecies appears to originate from changes in the relative replication kinetics of the large mutant spectrum present in the infected liver.