A Single Residue Influences the Reaction Mechanism of Ammonia Lyases and Mutases

All ways lead to Rome? Computer modeling and kinetic measurements identified a distinct residue in Phe/Tyr ammonia lyases (PAL/TAL) which controls whether the Friedel–Crafts or an E₁cB reaction mechanism takes place. Hence, Glu484 in pcPAL favors the Friedel–Crafts reaction (see picture, MIO=4‐methylidene imidazol‐5‐one) whereas an Asn in TAL gives an elimination reaction. These mechanistic investigations also reveal activity of a PAL mutant and a TAL towards an amino alcohol.

     

Exploring vision-related acupuncture point specificity with multivoxel pattern analysis

Acupoint specificity is one of the central issues of functional magnetic resonance imaging (fMRI) studies of acupuncture and has been under discussed. However, strong and consistent proof has not been provided for the existence of acupoint specificity, and unsuitable analysis approach applied could be the reason. We observed that previous researches of acupoint specificity were mostly based on model-based methods which were limited to make exploration of acupoint specificity because of the inaccurate specified prior. Here we applied multi-voxel pattern analysis (MVPA) to investigate the specificity of brain activation patterns induced by acupuncture stimulations at a vision-related acupoint (GB37) and a nearby nonacupoint (NAP). Results showed that multiple brain areas could differentiate the central neural response patterns induced by acupuncture stimulation at these two sites with higher accuracy above the chance level. These regions included occipital cortex, limbic-cerebellar areas and somatosensory cortex. Our results support that the characteristic neural response patterns of brain cortex to the acupuncture stimulation at GB37 and a nearby NAP could differ from each other effectively with the application of MVPA approach.     

基于受激辐射信号的谱域光学相干层析分子成像方法

鉴于不同生理病理状态下组织复折射率实部的变化不大,传统光学相干层析(OCT)成像技术在分子特异性识别上存在先天不足.为此,本文提出了基于受激辐射信号的OCT成像方法,可在实现传统散射成像的同时,实现基于受激辐射信号的分子成像.在超高分辨率谱域OCT系统的基础上,通过增设光谱分光与调制抽运光支路,建立了基于单宽谱光源的抽运探测谱域OCT系统,详细推导了调制抽运下受激辐射信号的获取与成像公式.利用搭建的抽运探测谱域OCT系统,实现了瞬态受激辐射信号的相干探测.基于同时获取的受激辐射OCT信号和传统OCT信号,成功重构了氮化物粉末构建样品的基于受激辐射信号的分子对比OCT图像.     

Origin of Thermal and Hyperthermal CO2 from CO Oxidation on Pt Surfaces: The Role of Post‐Transition‐State Dynamics,Active Sites,and Chemisorbed CO2

The post‐transition‐state dynamics in CO oxidation on Pt surfaces are investigated using DFT‐based ab initio molecular dynamics simulations. While the initial CO₂ formed on a terrace site on Pt(111) desorbs directly, it is temporarily trapped in a chemisorption well on a Pt(332) step site. These two reaction channels thus produce CO₂ with hyperthermal and thermal velocities with drastically different angular distributions, in agreement with recent experiments (Nature, 2018 , 558, 280–283). The chemisorbed CO₂ is formed by electron transfer from the metal to the adsorbate, resulting in a bent geometry. While chemisorbed CO₂ on Pt(111) is unstable, it is stable by 0.2 eV on a Pt(332) step site. This helps explain why newly formed CO₂ produced at step sites desorbs with far lower translational energies than those formed at terraces. This work shows that steps and other defects could be potentially important in finding optimal conditions for the chemical activation and dissociation of CO₂.     

The G553M Mutant of Peroxisomal Carnitine Octanoyltransferase Catalyses Acetyl Transfer and Acetyl-CoA Hydrolysis

Summary. The structure of carnitine acetyltransferase revealed a putative binding site for longer acyl chains but access was blocked by methionine 564 (G. Jogl and L. Tong (2003) Cell 112, 113–122). The equivalent residue in all long chain carnitine acyltransferases is a conserved glycine. Mutation of glycine 553 to methionine in bovine COT resulted in loss of activity with all acyl-CoA substrates except acetyl-CoA, supporting the hypothesis that the methionine blocks access for longer acyl chains. The kinetic characteristics of acetyl transfer to carnitine were identical in the native and mutant enzyme. However, rapid acetyl-CoA hydrolysis in the mutant but not the wild-type indicates perturbation of the catalytic site.     

What a Difference an OH Makes: Conformational Dynamics as the Basis for the Ligand Specificity of the Neomycin‐Sensing Riboswitch

To ensure appropriate metabolic regulation, riboswitches must discriminate efficiently between their target ligands and chemically similar molecules that are also present in the cell. A remarkable example of efficient ligand discrimination is a synthetic neomycin‐sensing riboswitch. Paromomycin, which differs from neomycin only by the substitution of a single amino group with a hydroxy group, also binds but does not flip the riboswitch. Interestingly, the solution structures of the two riboswitch–ligand complexes are virtually identical. In this work, we demonstrate that the local loss of key intermolecular interactions at the substitution site is translated through a defined network of intramolecular interactions into global changes in RNA conformational dynamics. The remarkable specificity of this riboswitch is thus based on structural dynamics rather than static structural differences. In this respect, the neomycin riboswitch is a model for many of its natural counterparts.     

The substrate specificity of a glucoamylase with steroidal saponin-rhamnosidase activity from Curvularia lunata

In previous work, we studied and reported that an enzyme from Curvularia lunata 3.4381 had the novel specificity to hydrolyze the terminal rhamnosyl at C-3 position of steroidal saponin and obtained four transformed products; the enzyme was purified and ascertained as glucoamylase (EC 3.2.1.3 GA). In this work, the enzyme exhibiting steroidal saponin-rhamnosidase activity was systematically studied on 21 steroidal saponins and 6 ginsenosides. The results showed that the α-1,2-linked end-rhamnosyl residues at C-3 position of steroidal saponins could be hydrolyzed to corresponding secondary steroidal saponins, among which 18 compounds were isolated and identified, including 3 new secondary compounds. For the furostanosides having glucosyl residues at the C-26 position, hydrolysis occurred first at end-rhamnosyl at C-3 position to produce secondary furostanosides. The reaction of hydrolyzing glucosyl at C-26 position depended considerably on longer reaction times yielding the corresponding secondary spirostanosides (without rhamnosyl and glucosyl residues). The enzyme had the strict specificity for the terminal α-1,2-linked rhamnosyl residues of linear chain, or the terminal α-1,2-linked rhamnosyl residues with branched chain of 1,4-linked glycosyl residues of sugar chain at C-3 position of steroidal saponins, it was not specific for different aglycones, different glycons, and the number of glycon of sugar chain of steroidal saponin. The end-rhamnosyl of ginsenosides and p-nitrophenyl-α-l-rhamnopyranoside (pNPR) could not be hydrolyzed by the enzyme from C. lunata.     

Ion Specificity on Electric Energy Generated by Flowing Water Droplets

The development of energy‐conversion devices using water movement has actively progressed. Ionovoltaic devices, which are driven by ion dynamics, show ion specificity by which different ions with identical charges show different output performance. However, the ion specificity remains poorly understood because the influence of the ion species on generated electric signals is not elucidated. The ion specificity in electric signals induced by flowing water droplet was investigated in terms of its relationship with the potential profile across the solid–liquid interface.     

Mechanistic studies of the oxidative coupling polymerization of phenols. VI. Comparison of reactivities of DMP,PPO-dimer,and -trimer in the copper-catalyzed oxidative coupling polymerization

In the oxidative coupling polymerization, catalyzed by copper-amine complexes, the oxidation rates of 2,6-dimethylphenol (DMP) and its C? O-coupled dimer [4-(2′,6′-dimethylphenoxy)-2,6-dimethylphenol] and trimer [4-(-4′-(2″,6″-dimethylphenoxy)-2′,6′-dimethylphenoxy))-2,6-dimethylphenol] have been determined. The DMP concentration dependence shows a Michaelis–Menten-type behavior. On the other hand, the dimer and trimer showed a first-order rate-dependence in the respective phenol concentrations. This indicates that the slow reaction step, following an equilibrium complex formation between DMP and copper complex, is relatively fast for both the dimer and the trimer. Therefore, coordination of dimer or trimer to the copper complex appears to be rate-determining. Furthermore, the dimer and trimer gave overall reaction rates approximately eight times higher than found for DMP. Following the Flory principle of equal reactivity for functional groups of oligomers in polycondensations, all PPO oligomers can be assumed to have equally high oxidation rates as the dimer and trimer. The yield of undesired DPQ side product is strongly reduced when starting with the dimer (0.18%), or trimer (0.17%), compared to 3.3% for DMP. This is not unexpected, since DPQ can only be formed from two monomeric DMP residues. In fact, using a 1/10 molar mixture of dimer/DMP already results in a DPQ yield of only 1.7%. Furthermore, when starting from DMP, it has been observed that DPQ was predominantly formed during the first 30% conversion. Starting from dimer (or trimer) DPQ was formed at an almost constant very low rate during the whole course of the reaction. From these experiments it can be concluded that the most important polymerization reaction involves oxidation of copper-coordinated DMP anion to its corresponding cations, followed by coupling with a copper coordinated PPO chain.