Enzyme Promiscuity in Enolase Superfamily. Theoretical Study of o-Succinylbenzoate Synthase Using QM/MM Methods

The promiscuous activity of the enzyme o-succinylbenzoate synthase (OSBS) from the actinobacteria Amycolatopsis is investigated by means of QM/MM methods, using both density functional theory and semiempirical Hamiltonians. This enzyme catalyzes not only the dehydration of 2-succinyl-6R-hydroxy-2,4-cyclohexadiene-1R-carboxylate but also catalyzes racemization of different acylamino acids, with N-succinyl-R-phenylglycine being the best substrate. We investigated the molecular mechanisms for both reactions exploring the potential energy surface. Then, molecular dynamics simulations were performed to obtain the free energy profiles and the averaged interaction energies of enzymatic residues with the reacting system. Our results confirm the plausibility of the reaction mechanisms proposed in the literature, with a good agreement between theoretical and experimentally derived activation free energies. Our simulations unravel the role played by the different residues in each of the two possible reactions. The presence of flexible loops in the active site and the selection of structural modifications in the substrate seem to be key elements to promote the promiscuity of this enzyme.This work was supported by the Spanish Ministerio de Economia y Competitividad project CTQ2012-36253-C03-03 ́ and FEDER funds. K.S. thanks the Polish National Science Center (NCN) for Grant 2011/02/A/ST4/00246. The authors acknowledge computational facilities of the Servei d’Informatica ̀ de la Universitat de Valencia in the ̀ “Tirant” supercomputer, which is part of the Spanish Supercomputing Network

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Fe-W supermirrors for polarizing neutrons

Polarized neutrons play an important role in scattering studies of condensed matter. Consequently, an efficient means of polarizing a neutron beam is very valuable. In addition to conventional, bulk single-crystal polarizers such as the Heusler alloy Cu{sub 2}MnAl, polarizing mirrors are often used for this purpose. Thin film bilayers of ferromagnetic Fe and nonmagnetic W have been deposited by sputtering on flat glass substreates according to a sequence of gradually varying bilayer thicknesses which in effect extends the critical angle for external mirror reflection for neutrons of one spin state when the Fe is magnetized in the plane of the film. The measured reflectivity of this Fe-W multilayer system is compared with that of other supermirror polarizers consisting of different materials and layer sequences. 14 refs., 3 figs

Allogeneic Transfusion after Predonation of Blood for Elective Spine Surgery

The literature suggests preoperative autologous blood donation in total joint arthroplasty is associated with increased overall transfusion rates compared with nondonation and is not cost-effective for all patients. We asked whether the amount of intraoperative blood loss and blood replacement differs between autologous donors and nondonors in elective spine surgery and whether the rates of allogeneic blood transfusions differ between the two groups; we then determined the cost of wasted predonated units. We retrospectively reviewed 676 patients who underwent elective lumbar spine surgery and compared relevant data to that in a matched cohort of 51 patients who predonated blood and 51 patients who received only cell-saver blood and underwent instrumented spinal fusion. Patients who predonated blood had similar blood loss as patients who did not predonate, but they had more blood replacement (1391 cc compared with 410 cc). Patients who predonated blood also had a lower preoperative hemoglobin level and wasted a half unit of blood on average. There was no major difference in allogeneic blood transfusion rates between the two groups. Our data suggest for short, instrumented lumbar fusion surgeries in patients with a normal coagulation profile, preoperative blood donation is not beneficial