Enzyme repurposing of a hydrolase as an emergent peroxidase upon metal binding

As an alternative to Darwinian evolution relying on catalytic promiscuity, a protein may acquire auxiliary function upon metal binding, thus providing it with a novel catalytic machinery. Here we show that addition of cupric ions to a 6-phosphogluconolactonase 6-PGLac bearing a putative metal binding site leads to the emergence of peroxidase activity (kcat7.8 × 10−2 s−1, KM 1.1 × 10−5 M). Both X-ray crystallographic and EPR data of the copper-loaded enzyme Cu·6-PGLacreveal a bis-histidine coordination site, located within a shallow binding pocket capable of accommodating the o-dianisidine substrate

Phase diagram and magnetocaloric effect of CoMnGe_{1-x}Sn_{x} alloys

We propose the phase diagram of a new pseudo-ternary compound, CoMnGe_{1-x}Sn_{x}, in the range x less than or equal to 0.1. Our phase diagram is a result of magnetic and calometric measurements. We demonstrate the appearance of a hysteretic magnetostructural phase transition in the range x=0.04 to x=0.055, similar to that observed in CoMnGe under hydrostatic pressure. From magnetisation measurements, we show that the isothermal entropy change associated with the magnetostructural transition can be as high as 4.5 J/(K kg) in a field of 1 Tesla. However, the large thermal hysteresis in this transition (~20 K) will limit its straightforward use in a magnetocaloric device.Comment: 12 pages, 5 figure

Advances in Thick GEM-like gaseous electron multipliers. Part I: atmospheric pressure operation

Thick GEM-like (THGEM) gaseous electron multipliers are made of standard printed-circuit board perforated with sub-millimeter diameter holes, etched at their rims. Effective gas multiplication factors of 100000 and 10000000 and fast pulses in the few nanosecond rise-time scale were reached in single- and cascaded double-THGEM elements, in atmospheric-pressure standard gas mixtures with single photoelectrons. High single-electron detection efficiency is obtained in photon detectors combining THGEMs and semitransparent UV-sensitive CsI photocathodes or reflective ones deposited on the top THGEM face; the latter benefits of a reduced sensitivity to ionizing background radiation. Stable operation was recorded with photoelectron fluxes exceeding MHz/mm2. The properties and some potential applications of these simple and robust multipliers are discussed.Comment: 41 pages, 27 figures. Submitted to Nucl. Instr. and Meth. A, Dec 21, 200

High-resolution microwave frequency dissemination on an 86-km urban optical link

We report the first demonstration of a long-distance ultra stable frequency dissemination in the microwave range. A 9.15 GHz signal is transferred through a 86-km urban optical link with a fractional frequency stability of 1.3x10-15 at 1 s integration time and below 10-18 at one day. The optical link phase noise compensation is performed with a round-trip method. To achieve such a result we implement light polarisation scrambling and dispersion compensation. This link outperforms all the previous radiofrequency links and compares well with recently demonstrated full optical links.Comment: 11 pages, 5 figure