Relationship between the composition of phospholipids and respiratory activity of choline-deficient mutants ofNeurospora crassa

Phosphatidylcholine is one of the most frequent phospholipid components of the inner mitochondrial membrane ofNeurospora crassa. Quantitative analysis of phospholipids of the wild strain ofNeurospora crassa and of its twocho mutants showed that these strains did not significantly differ in the content of phosphatidylcholine. Mutants cultivated in a medium without choline contained, as compared with the wild strain, an increased amount of phosphatidylserine and a decreased quantity of phosphatidic acid. Respiratory activity increased and sensitivity to inhibitors of respiration changed. It is likely that the presence of choline in the growth medium exerts a regulatory effect on the cell metabolism of these mutants.     

Dopamine receptors for every species: Gene duplications and functional diversification in Craniates

The neuromodulatory effects of dopamine on the central nervous system of craniates are mediated by two classes of G protein-coupled receptors (D1 and D2), each comprising several subtypes. A systematic isolation and characterization of the D1 and D2-like receptors was carried out in most of the Craniate groups. It revealed that two events of gene duplications took place during vertebrate evolution, before or simultaneously to the emergence of Gnathostomes. It led to the conservation of two-to-four paralogous receptors (subtypes), depending on the species. Additional duplication of dopamine receptor gene occurred independently in the teleost fish lineage. Duplicated genes were maintained in most of the vertebrate groups, certainly by the acquisition of a few functional characters, specific of each subtypes, as well as by discrete changes in their expression territories in the brain. The evolutionary scenario elaborated from these data suggests that receptor gene duplications were the necessary conditions for the expansion of vertebrate forebrain to occur, allowing dopamine systems to exert their fundamental role as modulator of the adaptive capabilities acquired by vertebrate species.     

Phosphatidylinositol-4,5-bisphosphate, PIP2, controls KCNQ1/KCNE1 voltage-gated potassium channels: a functional homology between voltage-gated and inward rectifier K+ channels

Phosphatidylinositol-4,5-bisphosphate (PIP(2)) is a major signaling molecule implicated in the regulation of various ion transporters and channels. Here we show that PIP(2) and intracellular MgATP control the activity of the KCNQ1/KCNE1 potassium channel complex. In excised patch-clamp recordings, the KCNQ1/KCNE1 current decreased spontaneously with time. This rundown was markedly slowed by cytosolic application of PIP(2) and fully prevented by application of PIP(2) plus MgATP. PIP(2)-dependent rundown was accompanied by acceleration in the current deactivation kinetics, whereas the MgATP-dependent rundown was not. Cytosolic application of PIP(2) slowed deactivation kinetics and also shifted the voltage dependency of the channel activation toward negative potentials. Complex changes in the current characteristics induced by membrane PIP(2) was fully restituted by a model originally elaborated for ATP-regulated two transmembrane-domain potassium channels. The model is consistent with stabilization by PIP(2) of KCNQ1/KCNE1 channels in the open state. Our data suggest a striking functional homology between a six transmembrane-domain voltage-gated channel and a two transmembrane-domain ATP-gated channel.     

A new cyclodextrin-agar medium for surface cultivation of microbes on lipophilic substrates

Summary Inclusion of cyclodextrins into an agar gel enabled a homogenous incorporation of water-immiscible lipophilic organic liquids and solids as substrates for surface microbial growth or conversion. Surface cultivation ofCandida lipolytica andC. tropicalis was demonstrated in and-cyclodextrin/hexadecane-agar media.     

Ethanol fermentation by ionically adsorbed Zymomomas mobilis: Environmental effects on cell immobilization

Batch ethanol fermentation by cells of Zymomomas mobilis ATCC 29191, ionically adsorbed on a DEAE-cellulose ion exchanger, was investigated in a stirred fermentor. Adsorption isotherms in different media were determined and used to interpret the effects of the environment on cell immobilization. Other factors affecting cell immobilization during an actual fermentation were studied. Mechanical agitation was found to cause detachment of cells from the ion exchange particles. The results suggest that the amount of cells adsorbed during a fermentation process is different from that found from adsorption isotherm data. Consequently, application of equilibrium adsorption data to actual fermentations should be done with caution.     

IGF-I and IGFBP-3 transport in the rat heart

Specific binding of IGF-binding protein (IGFBP)-3 was shown to be present in the isolated, beating rat heart. The uptake of perfused (125)I-labeled IGF-I in the beating heart was decreased to 9% by blocking IGF-I binding sites with the IGF-I analog Long R(3) (LR(3)) IGF-I. When LR(3) was perfused with complexes of (125)I-IGF-I. IGFBP-3, uptake of (125)I-IGF-I was decreased to 41%, which was significantly greater than LR(3) and (125)I-IGF-I (41 vs. 9%). These data suggest that both microvessel IGF-I and IGFBP-3 binding sites contribute to the transport of IGF-I in the perfused rat heart. This also suggests a novel and plausible mechanism whereby circulating IGFs reach sites of IGF bioactivity.     

Triterpene glycosides from Astragalus icmadophilus

Six cycloartane-type triterpene glycosides were isolated from Astragalus icmadophilus along with two known cycloartane-type glycosides, five known oleanane-type triterpene glycosides and one known flavonol glycoside. The structures of the six compounds were established as 3-O-[α-L-arabinopyranosyl-(1 → 2)-O-3-acetoxy-α-L-arabinopyranosyl]-6-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxycycloartane, 3-O-[α-L-rhamnopyranosyl-(1 → 2)-O-α-L-arabinopyranosyl-(1 → 2)-O-β-D-xylopyranosyl]-6-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxy cycloartane, 3-O-[α-L-arabinopyranosyl-(1 → 2)-O-3,4-diacetoxy-α-L-arabinopyranosyl]-6-O-β-D-glucopyranosyl-3β,6α,16β,24(S),25-pentahydroxycycloartane, 3-O-[α-L-arabinopyranosyl-(1 → 2)-O-3-acetoxy-α-L-arabinopyranosyl]-6-O-β-D-glucopyranosyl-3β,6α,16β,25-tetrahydroxy-20(R),24(S)-epoxycycloartane, 3-O-[α-L-arabinopyranosyl-(1 → 2)-O-β-D-xylopyranosyl]-6-O-β-D-glucopyranosyl-3β,6α,16β,24α-tetrahydroxy-20(R),25-epoxycycloartane, 3-O-[α-L-rhamnopyranosyl-(1 → 2)-O-α-L-arabinopyranosyl-(1 → 2)-O-β-D-xylopyranosyl]-6-O-β-D-glucopyranosyl-3β,6α,16β,24α-tetrahydroxy-20(R),25-epoxycycloartane by the extensive use of 1D- and 2D-NMR experiments along with ESIMS and HRMS analysis.The first four compounds are cyclocanthogenin and cycloastragenol glycosides, whereas the last two are based on cyclocephalogenin as aglycone, more unusual in the plant kingdom, so far reported only from Astragalus spp.     

A mixture-model approach for parallel testing for unequal variances

Testing for unequal variances is usually performed in order to check the validity of the assumptions that underlie standard tests for differences between means (the t-test and anova). However, existing methods for testing for unequal variances (Levene's test and Bartlett's test) are notoriously non-robust to normality assumptions, especially for small sample sizes. Moreover, although these methods were designed to deal with one hypothesis at a time, modern applications (such as to microarrays and fMRI experiments) often involve parallel testing over a large number of levels (genes or voxels). Moreover, in these settings a shift in variance may be biologically relevant, perhaps even more so than a change in the mean. This paper proposes a parsimonious model for parallel testing of the equal variance hypothesis. It is designed to work well when the number of tests is large; typically much larger than the sample sizes. The tests are implemented using an empirical Bayes estimation procedure which `borrows information' across levels. The method is shown to be quite robust to deviations from normality, and to substantially increase the power to detect differences in variance over the more traditional approaches even when the normality assumption is valid.     

Role of mutation Y6F on the binding properties of Schistosoma japonicum glutathione S-transferase

The role of the hydroxyl group of tyrosine 6 in the binding of Schistosoma japonicum glutathione S-transferase has been investigated by isothermal titration calorimetry (ITC). A site-specific replacement of this residue with phenylalanine produces the Y6F mutant, which shows negative cooperativity for the binding of reduced glutathione (GSH). Calorimetric measurements indicated that the binding of GSH to Y6F dimer is enthalpically driven over the temperature range investigated. A concomitant net uptake of protons upon binding of GSH to Y6F mutant was detected carrying out calorimetric experiments in various buffer systems with different heats of ionization. The entropy change is favorable at temperatures below 26 °C for the first site, being entropically favorable at all temperatures studied for the second site. The enthalpy change of binding is strongly temperature-dependent, arising from a large negative ΔC°_p1=−3.45±0.62 kJ K⁻¹ mol⁻¹ for the first site, whereas a small ΔC°_p2=−0.33±0.05 kJ K⁻¹ mol⁻¹ for the second site was obtained. This large heat capacity change is indicative of conformational changes during the binding of substrate.     

Experimental studies on the mechanism of the nitroglycerin effect.

The regional decrease of the speed and extent of the contraction and the relaxation of the canine myocardium induced by coronary ligation was enhanced by intravenously administered nitroglycerin (GTN), simultaneously with the decrease of the left ventricular pressure, while the increase of myocardial fiber length caused by that procedure was partly abolished. The above changes could be reproduced by GTN applied directly onto the ischaemic myocardial surface even before the decrease of the left ventricular pressure. These changes induced by GTN might play a role in the decrease or abolishment of regional asynergic wall motion.