Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Microwave optical double resonance and reanalysis of the CaF AΠr-XΣ band system

A laser excitation spectrum of the (0,0) and (1,1) bands of the CaF A²Π-X²Σ system has been recorded and all 12 rotational branches assigned on the basis of laser induced fluorescence measurements. Microwave optical double resonance (MODR) measurements were also made on several low-J transitions to obtain precise spectroscopic constants of the X²Σ state. The present set of molecular constants for both the A²Π and X²Σ states represent a vast improvement in precision over previously reported values because of the larger number of line position measurements and the use of a more reasonable Hamiltonian. The excellent agreement between the rotational constants derived from the optical and microwave measurements fully validates the assignments. Important derived constants are listed below (in cm⁻¹) with 95% confidence limits in parentheses.     

The visible spectrum of fulvene

Vapour phase and mixed crystal of the visible band system of fulvene are reported. The spectra show several interesting features including a main progression of 660 cm^?1 corresponding to the out-of-plane methylene twisting vibration. Strong Herzberg—Teller origins together with the breadth and overall diffuseness indicate two electronic states of symmetry A₁ and B₂ may be responsible for the observed spectrum. The spectra are blue shifted in going from the vapour to mixed crystal and show sequence structure to the blue of the main bands in the vapour phase.     

Computable error bounds for pointwise derivatives of a Neumann problem

In this paper we discuss the recovery of derivatives and thecomputation of rigorous and useful upper bounds for the pointwiseerror in the recovered derivatives, for finite element approximationsof the Laplace equation with Neumann boundary conditions, especiallyat points close to or on a smooth, curved boundary. We analyzethe dipole image technique for the case of curved boundaries,and show how to compute reliable recovered derivatives and errorbounds even in the limiting case of points lying on the curvedboundary. Numerical experiments show reasonably tight errorbounds for points both close to and away from a curved boundary.     

The microwave spectrum and structure of fulvene

The microwave spectra of four ¹³C and two monodeutero species of fulvene have been recorded and analysed. Earlier data for the parent species has also been slightly refined. The final structure which emerges for fulvene is essentially three weakly coupled ethylenic entities with bond lengths: C₁C₂ = 1.470Å C₂C₃ = 1.355Å, C₃C₄ = 1.476Å and C₁C₆ = 1.3485Å. The CH bond distances and ring angles are close to expected values.     

Hepatitis C virus NS3 protease requires its NS4A cofactor peptide for optimal binding of a boronic acid inhibitor as shown by NMR

NMR spectroscopy was used to characterize the hepatitis C virus (HCV) NS3 protease in a complex with the 24 residue peptide cofactor from NS4A and a boronic acid inhibitor, Ac-Asp-Glu-Val-Val-Pro-boroAlg-OH. Secondary-structure information, NOE constraints between protease and cofactor, and hydrogen-deuterium exchange rates revealed that the cofactor was an integral strand in the N-terminal beta-sheet of the complex as observed in X-ray crystal structures. Based upon chemical-shift perturbations, inhibitor-protein NOEs, and the protonation state of the catalytic histidine, the boronic acid inhibitor was bound in the substrate binding site as a transition state mimic. In the absence of cofactor, the inhibitor had a lower affinity for the protease. Although the inhibitor binds in the same location, differences were observed at the catalytic site of the protease.     

Cycloaddition of delta2-thiazolines and acyl ketenes under acidic conditions results in bicyclic 1,3-oxazinones and not 6-acylpenams as earlier reported

[reaction: see text] Optically active Delta(2)-thiazolines 4 were previously reported to react with acyl Meldrum's acid derivatives 5 under acidic conditions (HCl (g) in benzene) to stereoselectively give 6-acylpenams 1. Recently we have discovered that the structure elucidation of these compounds was incorrect. Thus, we report new data showing that instead of acyl beta-lactams, the optically active isomers 3R,9R-1,3-oxazinones 3a-g are obtained stereoselectively in 38-93% yields.