What to Learn from a Comparative Genomic Sequence Analysis of <Emphasis Type="Italic">L</Emphasis>-Carnitine Dehydrogenase

Summary. In contrast to eukaryotic cells certain eubacterial strains have acquired the ability to utilize L-carnitine (R-(–)-3-hydroxy-4-(trimethylamino)butyrate) as sole source of energy, carbon and nitrogen. The first step of the L-carnitine degradation to glycine betaine is catalysed by L-carnitine dehydrogenase (L-CDH, EC 1.1.1.108) and results in the formation of the dehydrocarnitine. During the oxidation of L-carnitine a simultaneous conversion of the cofactor NAD⁺ to NADH takes place. This catabolic reaction has always been of keen interest, because it can be exploited for spectroscopic L-carnitine determination in biological fluids – a quantification method, which is developed in our lab – as well as L-carnitine production.Based on a cloned L-CDH sequence an expedition through the currently available prokaryotic genomic sequence space began to mine relevant information about bacterial L-carnitine metabolism hidden in the enormous amount of data stored in public sequence databases. Thus by means of homology-based and context-based protein function prediction is revealed that L-CDH exists in certain eubacterial genomes either as a protein of approximately 35 kDa or as a homologous fusion protein of approximately 54 kDa with an additional putative domain, which is predicted to possess a thioesterase activity. These two variants of the enzyme are found on one hand in the genome sequence of bacterial species, which were previously reported to decompose L-carnitine, and on the other hand in gram-positive bacteria, which were not known to express L-CDH. Furthermore we could not only discover that L-CDH is located in a conserved genetic entity, which genes are very likely involved in this L-carnitine catabolic pathway, but also pinpoint the exact genomic sequence position of several other enzymes, which play an essential role in the bacterial metabolism of L-carnitine precursors.     

Electron exchange in the tetracyanoquinodimethane system: Unexpected dependence on solvent polarity and viscosity

The electron transfer rate between tetracyanoquinodimethane and its radical anion is measured for different solvents and temperatures using ESR line broadening. The solvent polarity term γ = 1/n² - 1/ε (n is the refractive index, ε the dielectric constant) could be changed in the range 0.05 ≤ γ ≤ 0.53. The true rate constants k (corrected for diffusion) are discussud in terms of the classical theory of electron transfer. A linear dependence of ln k on γ is only found with a viscosity-dependent pre-exponential factor. The outer reorganization energy is small compared with the inner and has a negative sign. This is explained by the special arrangement of the ellipsoidal reactants in the activated complex.     

Synthese und Konfigurationszuordnung von potentiell antimikrobiellen 5,6-Dihydroxyisobenzofuranonen

Summary Oxidation of isobenzofuranone1 yielded in a diastereoselective reaction epoxide2. Acidolysis of2 resulted in a mixture oftrans-glycols6 a (88%) and7 a (4%), which were separated by crystallization. The relative configuration of6 a and7 a at the chiral centers 3 a, 5, 6, and 7 a was determined by¹H-NMR-spectroscopy and X-ray analysis of O-acetylated and 7 a-methylated derivatives.

     

Average growth-behavior and distribution properties of generalized weighted digit-block-counting functions

We introduce a generalized weighted digit-block-counting function on the nonnegative integers, which is a generalization of many digit-depending functions as, for example, the well known sum-of-digits function. A formula for the first moment of the sum-of-digits function has been given by Delange in 1972. In the first part of this paper we provide a compact formula for the first moment of the generalized weighted digit-block-counting function and show that a (weak) Delange type formula holds if the sequence of weights converges. The question, whether the converse is true as well, can only be answered partially at the moment. In the second part of this paper we study distribution properties of generalized weighted digit-block-counting sequences and their d-dimensional analogues. We give an if and only if condition under which such sequences are uniformly distributed modulo one.     

Katalysatoren für die Sonnenenergie

Die Entwicklung der künstlichen Photosynthese und somit die mehr oder minder direkte Nutzung der Sonnenenergie ist seit Jahren ein zentrales Thema. Wie kann man Sonnenenergie billiger und besser zugänglich machen? Konkrete Empfehlungen für die zukünftige Forschung sprechen Wissenschaftler nach dem ersten Chemical Sciences and Society Symposium (CS3) zur Nutzung von Sonnenlicht aus.     

Coulomb and photo cross sections for nucleon emission from relativistic O projectiles

Coulomb cross sections for nucleon emission out of ¹⁶O projectiles scattered with laboratory energies of 2.1, 60 and 200 GeV/nucleon on various target nuclei are calculated in first-order perturbation theory by using the corresponding photo cross sections. The photo cross sections are obtained with an 1-particle-1-hole basis in the giant resonance region and with the quasi-deuteron model up to photon energies of 140 MeV. Whereas the 2.1 GeV/nucleon results agree well with the experimental data points, the 60 and 200 GeV/nucleon cross sections are roughly one quarter lower than the measured ones, because also photons with energies higher than 140 MeV contribute at these incident energies.