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Class II fructose 1,6-bisphosphate aldolases (FBP-aldolases) catalyse the zinc-dependent, reversible aldol condensation of dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P) to form fructose 1,6-bisphosphate (FBP). Analysis of the structure of the enzyme from Escherichia coli in complex with a transition state analogue (phosphoglycolohydroxamate, PGH) suggested that substrate binding caused a conformational change in the beta5-alpha7 loop of the enzyme and that this caused the relocation of two glutamate residues (Glu181 and Glu182) into the proximity of the active site. Site-directed mutagenesis of these two glutamate residues (E181A and E182A) along with another active site glutamate (Glu174) was carried out and the mutant enzymes characterised using steady-state kinetics. Mutation of Glu174 (E174A) resulted in an enzyme which was severely crippled in catalysis, in agreement with its position as a zinc ligand in the enzyme's structure. The E181A mutant showed the same properties as the wild-type enzyme indicating that the residue played no major role in substrate binding or enzyme catalysis. In contrast, mutation of Glu182 (E182A) demonstrated that Glu182 is important in the catalytic cycle of the enzyme. Furthermore, the measurement of deuterium kinetic isotope effects using [1(S)-(2)H]DHAP showed that, for the wild-type enzyme, proton abstraction was not the rate determining step, whereas in the case of the E182A mutant this step had become rate limiting, providing evidence for the role of Glu182 in abstraction of the C1 proton from DHAP in the condensation direction of the reaction. Glu182 lies in a loop of polypeptide which contains four glycine residues (Gly176, Gly179, Gly180 and Gly184) and a quadruple mutant (where each glycine was converted to alanine) showed that flexibility of this loop was important for the correct functioning of the enzyme, probably to change the microenvironment of Glu182 in order to perturb its pK(a) to a value suitable for its role in proton abstraction. These results highlight the need for further studies of the dynamics of the enzyme in order to fully understand the complexities of loop closure and catalysis in this enzyme.

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The phase behavior of a mesogenic lattice-gas model consisting of freely rotating spins located at the sites of a three-dimensional cubic lattice has been studied using grand canonical Monte Carlo simulations. When two neighboring sites are occupied, the spin vectors interact via the extensively studied anisotropic Lebwohl-Lasher potential, plus an isotropic term of variable strength. The interaction between occupied and empty sites and two empty sites is taken to be zero. If the parameter governing the strength of the isotropic term is zero, the model exhibits an isotropic fluid-nematic transition, which becomes increasingly stronger as the temperature is lowered. The additional isotropic term is found to be important if the model is to reproduce experimental phase behavior, that is, to exhibit both nematic-vapor coexistence at low temperature and isotropic-vapor coexistence at higher temperatures.

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There have been a limited number of studies assessing the impact of attending physician supervision of residents in the emergency department (ED). The objective of this study is to describe the changes in patient care when attending emergency physicians (AEPs) supervise nonemergency medicine residents in a university hospital ED. This was a prospective study including 1,000 patients, 32 second- and third-year nonemergency medicine residents and eight AEPs. The AEPs classified changes in care for each case as major, minor, or none, according to a 40-item data sheet list. There were 153 major changes and 353 minor changes by the AEP. The most common major changes were ordering laboratory or x-ray tests that showed a clinically significant abnormality, and eliciting important physical exam findings. Potentially limb- or life-threatening errors were averted by the AEP in 17 patients. Supervision of nonemergency medicine residents in the ED resulted in frequent and clinically important changes in patient care.

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An Aspergillus nidulans DNA fragment composed of two adjacent SalI subfragments (1.8 and 0.85 kb) that carries an argB gene complementing the yeast arg3 mutation has been isolated from two different gene libraries. Hybridization results and immunological tests indicate that the cloned fragment contains the A. nidulans structural gene coding for ornithine carbamoyltransferase (OTCase). Using the cloned gene as a probe, the specific mRNA was identified. The level of this RNA observed in A. nidulans strains grown under various conditions correlated with the level of the OTCase activity, suggesting transcriptional control of OTCase synthesis. Expression of the cloned gene in Saccharomyces cerevisiae does not depend on its orientation in the vector. In Escherichia coli, the cloned gene does not function; however arg- transformants revert to prototrophy with high frequency possibly due to DNA rearrangements within the recombinant plasmid.

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