STD‐NMR‐Based Protein Engineering of the Unique Arylpropionate‐Racemase AMDase G74C

Structure‐guided protein engineering achieved a variant of the unique racemase AMDase G74C, with 40‐fold increased activity in the racemisation of several arylaliphatic carboxylic acids. Substrate binding during catalysis was investigated by saturation‐transfer‐difference NMR (STD‐NMR) spectroscopy. All atoms of the substrate showed interactions with the enzyme. STD‐NMR measurements revealed distinct nuclear Overhauser effects in experiments with and without molecular conversion. The spectroscopic analysis led to the identification of several amino acid residues whose substitutions increased the activity of G74C. Single amino acid exchanges increased the activity moderately; structure‐guided saturation mutagenesis yielded a quadruple mutant with a 40 times higher reaction rate. This study presents STD‐NMR as versatile tool for the analysis of enzyme–substrate interactions in catalytically competent systems and for the guidance of protein engineering.     

Motion of segment dislocations as a model for glass relaxation

Summary The meander model of polymer melts assumes nearly parallel packing of molecular chains and therefore invites to describe shear deformation processes by dislocation motion in analogy to metals. Examination of the glass relaxation data for 12 amorphous polymers leads to reasonable values for the energy and the Burgers vector of segment dislocations which are also consistent with thermal properties of the glass transition.Presented at the Third International Seminar on Polymer Physics Molecular Mobility and Energy Transfer in Polymer Systems, High Tatra, CSSR, April 1982     

Low current plasma effect optical switch on InP

Optical InP-GaInAsP directional coupler switches with a total length of 2 mm have been fabricated and operated by carrier injection. Switching is achieved at a very low injection current of 4 mA. For both switching states a crosstalk suppression exceeding 20 dB is obtained. In addition, the insertion loss estimated from the loss contributions of waveguides, bends and free carriers is as low as 1.3 dB.<>     

First Principles Investigation of Local Distortions in Doped La2CuO4

We present the results of first-principles cluster calculations of local distortions in doped La₂CuO₄. Local deformations of the CuO₆ octahedra associated with the presence of an additional extrinsic hole were determined using the density-functional (DF) method on various cluster models. The results indicate that a localized hole induces a contraction of the CuO(apical) distance from 2.40 to 2.28 Å. The contracted distance is in very good agreement with the anomalous, short CuO(apical) distance of 2.3 Å, observed recently by polarized Cu K-edge extended x-ray absorption fine structure (EXAFS) in La_1.85Sr_0.15CuO₄ and associated with the hole-rich stripe region.     

Two types of modified cardiac Na+ channels after cytosolic interventions at the alpha-subunit capable of removing Na+ inactivation

Repeated oesophageal acidification is a definitive feature of gastro-oesophageal reflux disease, which in turn is caused by relaxation of the lower oesophageal sphincter (LOS). This study in anaesthetised ferrets investigates the reflex pathways involved in effects of oesophageal acidification on motor function of the LOS, with particular focus on the role of tachykinins. LOS pressure was monitored with a perfused micromanometric sleeve assembly. Oesophageal acidification reduced LOS pressure by 48 +/- 5% until washout with saline. This reduction became larger with repeated tests, and was unaffected in amplitude by acute bilateral vagotomy, although the response became slower in onset. Intra-oesophageal capsaicin (0.5% solution) caused a 68 +/- 17% decrease in LOS pressure which remained unchanged with repeated tests. The NK-1 receptor antagonist CP96,345 (1-5 mg/kg intravenous (i.v.) blocked the post-vagotomy LOS responses to both intra-luminal acid and capsaicin. Close intra-arterial (i.a.) injections of capsaicin (1-100 micrograms) gut induced LOS relaxation which was neither vagally nor NK-1 receptor-mediated. Substance P or the selective NK-1 receptor agonist [Sar9, Met(O2)11] substance P (25-500 ng close i.a.) caused a biphasic LOS response, consisting of initial brief contraction followed by prolonged, dose-dependent relaxation. Tetrodotoxin (10 micrograms/kg close i.a.) changed the biphasic response to substance P to excitation only. The neurokinin-1 (NK-1) receptor antagonist CP96,345 (0.3-10 mg/kg i.v.) dose-dependently reduced the inhibitory response to substance P. The excitatory phase of the response to substance P was larger and prolonged after guanethidine (5 mg/kg, i.v.), or propranolol (1 mg/kg, i.v.). L-NAME (100 mg/kg i.v.) reduced the inhibitory phase. The selective NK-2 receptor agonist [beta-Ala8] neurokinin A(4-10) caused LOS excitation only. These data indicate that intra-oesophageal acid causes substance P release from extrinsic afferent nerve endings which activates local inhibitory pathways to the LOS via NK-1 receptors.     

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