Effect of pH and Monovalent Cations on the Formation of Quinonoid Intermediates of the Tryptophan Synthase α2β2 Complex in Solution and in the Crystal

Quinonoid intermediates play a key role in the catalytic mechanism of pyridoxal 5'-phosphate-dependent enzymes. Whereas the structures of other pyridoxal 5'-phosphate-bound intermediates have been determined, the structure of a quinonoid species has not yet been reported. Here, we investigate factors controlling the accumulation and stability of quinonoids formed at the beta-active site of tryptophan synthase both in solution and the crystal. The quinonoids were obtained by reacting the alpha-aminoacrylate Schiff base with different nucleophiles, focusing mainly on the substrate analogs indoline and beta-mercaptoethanol. In solution, both monovalent cations (Cs(+) or Na(+)) and alkaline pH increase the apparent affinity of indoline and favor accumulation of the indoline quinonoid. A similar pH dependence is observed when beta-mercaptoethanol is used. As indoline and beta-mercaptoethanol exhibit very distinct ionization properties, this finding suggests that nucleophile binding and quinonoid stability are controlled by some ionizable protein residue(s). In the crystal, alkaline pH favors formation of the indoline quinonoid as in solution, but the effect of cations is markedly different. In the absence of monovalent metal ions the quinonoid species accumulates substantially, whereas in the presence of sodium ions the accumulation is modest, unless alpha-subunit ligands are also present. Alpha-subunit ligands not only favor the formation of the intermediate, but also reduce significantly its decay rate. These findings define experimental conditions suitable for the stabilization of the quinonoid species in the crystal, a critical prerequisite for the determination of the three-dimensional structure of this intermediate

Blind Adaptive Chromatic Dispersion Compensation and Estimation for DSP-Based Coherent Optical Systems

We propose an accurate and low-complexity blind adaptive algorithm for chromatic dispersion (CD) compensation and estimation in coherent optical systems. The method is based on a Frequency Domain Equalizer (FDE), a low complexity Time Domain Equalizer arranged in a butterfly structure (B-TDE) and an Optical Performance Monitoring (OPM) block in a loop configuration. The loop is such that, at each iteration, the CD value compensated by the B-TDE and estimated by the OPM is given to the FDE; according to this estimation, in the subsequent iteration, the FDE compensates also this quantity. The procedure is repeated until the majority of CD is compensated by the FDE and a small residual quantity is compensated by a low complexity B-TDE with a small number of taps. The method is extended to long haul uncompensated links exploiting the information on the mean square error (MSE) provided by the B-TDE. The proposed algorithm is then experimentally validated for a polarization multiplexed quadrature phase shift keying (PM-QPSK) signal at 112 Gbit/s propagating along 1000 km of uncompensated Z PLUS® optical fiber. A statistical analysis of the performance of the proposed solution, in terms of mean value and standard deviation of the CD estimation error, is carried out, running a set of simulations including different impairments, such as noise, polarization dependent loss, polarization mode dispersion and self-phase modulation in a line of 1000 km of uncompensated G.652 optical fiber. Our method could be used to compensate and estimate any CD quantity without increasing the number of taps in the B-TDE and exploiting devices already included in the system (TDE, FDE and OPM) arranged in a loop

Morcegos em área de restinga de unidade de conservação no estado do Rio de Janeiro, sudeste do Brasil

Restingas are naturally fragile ecosystems, mainly because of instability of their soils, and, in addition, they have been constantly modified by human activities. This ecosystem is poorly investigated and information about its fauna is scarce. Consequently, little is known about bat communities in restingas, since most studies on bats occurred in fragments of Atlantic Forest. The aim of this study was to analyze the composition, species richness and abundance of bats from restingas of a conservation unit in southeastern Brazil (Área de Proteção Ambiental de Maricá), located in the state of Rio de Janeiro. In May 2011 and December 2013, we performed a total of 18 samplings with mist nets resulting in a sampling effort of 17,640 m2.h and the capture of 56 specimens of six Phyllostomidae bat species. Most captured species were of frugivorous bats. Artibeus lituratus was the most abundant species (39%). Despite the high degradation level of the studied area, the results of this study suggest that the area shows favorable attributes for the occurrence of bat species.Keywords: abundance, species composition, species richness, Atlantic Forest.Restingas são ecossistemas frágeis, devido à natureza instável de seu solo e, além disso, têm sido constantemente destruídas pelas atividades do homem. Esse ecossistema é um dos menos conhecidos e estudados dentro do bioma Mata Atlântica no tocante à fauna. Informações sobre as comunidades de morcegos e sobre suas interações ecológicas em restingas são escassas, sendo a maioria dos dados proveniente de estudos em fragmentos florestais de Mata Atlântica. Nesse sentido, o objetivo deste estudo foi analisar a composição, a riqueza de espécies e a abundância de morcegos da restinga da Área de Proteção Ambiental de Maricá, localizada no estado do Rio de Janeiro, sudeste do Brasil. Em maio de 2011 e dezembro de 2013, foi realizado um total de 18 noites de amostragem com redes de neblina que resultaram em 17.640 m².h de esforço amostral e em 56 indivíduos capturados, distribuídos em seis espécies da família Phyllostomidae. O maior número de capturas ocorreu para as espécies frugívoras, sendo Artibeus lituratus a mais abundante (39%). Apesar do elevado grau de degradação da área de estudo, os resultados do presente estudo sugerem que essa área ainda possui atributos favoráveis para a ocorrência de espécies de morcegos.Palavras-chave: abundância, composição de espécies, riqueza de espécies, Mata Atlântica

Accurate BER Estimation for Coherent Optical Transmission Systems

We propose a bit error rate (BER) estimation technique based on the analysis of the statistical distribution of the constellation points after electronic equalization. The method is successfully tested in presence of linear transmission impairments by both numerical simulations and experimental measurements

Serine racemase: a key player in neuron activity and in neuropathologies

Serine racemase is the pyridoxal 5’-phosphatedependent enzyme that catalyzes L-serine racemisation to D-serine, and L- and D-serine beta-elimination in mammalian brain. D-serine is the essential co-agonist of the N-methyl-D-aspartate receptor, that mediates neurotransmission, synaptic plasticity, cell migration and long term potentiation. High and low D-serine levels have been associated with distinct neuropathologies, agingrelated deficits and psychiatric disorders due to either hyper- or hypo-activation of the receptor. Serine racemase dual activity is regulated by ATP, divalent cations, cysteine nitrosylation, post-translational modifications, and interactions with proteins that bind either at the N- or Cterminus. A detailed elucidation of the molecular basis of catalysis, regulation and conformational plasticity, as well as enzyme and D-serine localization and neurons and astrocytes cross-talk, opens the way to the development of enzyme inhibitors and effectors for tailored therapeutic treatments