Atomic adsorption of oxygen on Cu(111) and Cu(110)

We have studied angle-resolved inverse photoemission ( = 9.7 eV) after room temperature adsorption of oxygen on Cu(111) and Cu(110). On Cu(111) exposure to 500 L induces a band (3.0 eV aboveE _F at) which shows clear dispersion (1.0 eV) to higher energies for off normal incidence. Since no LEED superstructure is seen for that system, our results present strong evidence for the presence of short-range surface order. Two adsorbate bands are identified (2.8 eV and 6.3 eV at) on Cu(110)p(2×1)-O. Our results are in good agreement with a long-bridge adsorption site.     

THEORETICAL ASPECTS OF THE U.V. INACTIVATION OF PROTEINS CONTAINING DISULFIDE BONDS

Equations are proposed for the estimation of quantum yields for cystine destruction and disulfide protein inactivation during u.v.-irradiation in acidic and neutral solutions. The formulas permit a discussion of energy transfer from excited aromatic amino acids to cystines and/or of chemical reactions between excited tryptophans or tyrosines and cystines. The results are discussed with regard to general aspects of the photo-biochemistry of enzymes.     

Alkali metal oxides: Occupied,unoccupied and excited states

The occupied and unoccupied electronic states of NaO₂ and KO₂ have been investigated by UV photoemission spectroscopy and inverse photoemission spectroscopy, respectively. In addition single electron excitations from occupied into empty levels have been probed by x-ray absorption and electron energy loss spectroscopy. The experimental data are augmented by LCGTO-X model cluster calculations. A detailed assignment of initial and final states is given. The excitation cross sections and an inversion of the ligand field induced3d level splitting in NaO₂ are discussed.     

Simultaneous detection of protein phosphorylation and acetylation by high-resolution NMR spectroscopy

Post-translational protein modifications (PTMs) such as phosphorylation and acetylation regulate a large number of eukaryotic signaling processes. In most instances, it is the combination of different PTMs that "encode" the biological outcome of these covalent amendments in a highly dynamic and cell-state-specific manner. Most research tools fail to detect different PTMs in a single experiment and are unable to directly observe dynamic PTM states in complex environments such as cell extracts or intact cells. Here we describe in situ observations of phosphorylation and acetylation reactions by high-resolution liquid-state NMR spectroscopy. We delineate the NMR characteristics of progressive lysine acetylation and provide in vitro examples of joint phosphorylation and acetylation events and how they can be deciphered on a residue-specific basis and in a time-resolved and quantitative manner. Finally, we extend our NMR investigations to cellular phosphorylation and acetylation events in human cell extracts and demonstrate the unique ability of NMR spectroscopy to simultaneously report the establishment of these PTMs by endogenous cellular enzymes.     

Signal and background separation

In many areas of research the measured spectra consist of a collection of "peaks"--the sought-for signals--which sit on top of an unknown background. The subtraction of the background in a spectrum has been the subject of many investigations and different techniques, varying from filtering to fitting polynomial functions, have been developed. These techniques yield results that are not always satisfactory and often even misleading. Based upon the rules of probability theory, we derive a formalism to separate the background from the signal part of a spectrum in a rigorous and self-consistent manner. We compare the results of the probabilistic approach to those obtained by two commonly used methods in an analysis of particle induced x-ray emission spectra.     

(S,S)-2,3-Dihydroxy-2,3-dihydrobenzoic acid: microbial access with engineered cells of Escherichia coli and application as starting material in natural-product synthesis

Cyclohexadiene-trans-5,6-diols such as (S,S)-2,3-dihydroxy-2,3-dihydrobenzoic acid (2,3-trans-CHD) have been shown to be of importance as chiral starting materials for the syntheses of bioactive substances, especially for the syntheses of carbasugars. By using methods of metabolic-pathway engineering, the Escherichia coli genes entB and entC, which encode isochorismatase and isochorismate synthase, were cloned and over-expressed in E. coli strains with a deficiency of entA, which encodes 2,3-dihydroxybenzoate synthase. A 30-fold increase in the corresponding EntB/EntC enzyme activities affects the accumulation of 2,3-trans-CHD in the cultivation medium. Although the strains did not contain deletions in chorismate-utilising pathways towards aromatic amino acids, neither chorismate nor any other metabolic intermediates were found as by-products. Fermentation of these strains in a 30 L pH-controlled stirred tank reactor showed that 2,3-trans-CHD could be obtained in concentrations of up to 4.6 g L(-1). This demonstrates that post-chorismate metabolites are accessible on a preparative scale by using techniques of metabolic-pathway engineering. Isolation and separation from fermentation salts could be performed economically in one step through anion-exchange chromatography or, alternatively, by reactive extraction. Starting from 2,3-trans-CHD as an example, we established short syntheses towards new carbasugar derivatives.     

Decomposition of multicomponent mass spectra using Bayesian probability theory

We present a method for the decomposition of the mass spectra of mixed gases using Bayesian probability theory. The method works without any calibration measurement and therefore applies also to the analysis of spectra containing unstable species. For the example of mixtures of three different hydrocarbon gases the algorithm provides concentrations and cracking coefficients of each mixture component and also their confidence intervals. The amount of information needed to obtain reliable results and its relation to the accuracy of our analysis are discussed.