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A Klemm

Publications and source records attributed to A Klemm.

27 records · Page 2Linked to original sources
PubMed1993

Determination, purification, and characterization of alpha-NADH.

alpha-NADH can be determined in the presence of high concentrations of beta-NADH using anion exchange HPLC combined with oxidation of beta-NADH by lactate dehydrogenase. The method is suited for the detection of a large number of impurities. Residual absorption is a poor measure of alpha-NADH. By combination of preparative anion exchange chromatography and reversed-phase HPLC, alpha-NADH can be prepared with 95-98% purity starting from beta-NADH. Commercially available preparations contain only 80-90% alpha-NADH. The anomerization kinetics of alpha- and beta-NADH has been investigated at pH 7.0 and 7.3 taking into account the irreversible conversion reactions of alpha- and beta-NADH. The H+ ion activity related anomerization rate constants kappa 1 (alpha to beta) and kappa 2 (beta to alpha) have been found to be 170 and 29 M-1 s-1, respectively, at pH 7.0 and 192 and 36 M-1 s-1, respectively, at pH 7.3. The equilibrium constants kappa 1 /kappa 2 are 5.8 and 5.3 at pH 7.0 and pH 7.3, respectively. Absorption and fluorescence properties of alpha-NADH preparations have been determined newly. At 25 degrees C, maximum absorption was found at 260.1 and 346.6 nm, whereas at 37 degrees C the wavelengths were 260.1 and 345.3 nm. Maximum fluorescence excitation was found at 348 nm, and maximum emission was at 453 nm.

Anions↗
PubMed1975

Amino-acid sequence of lac repressor from Escherichia coli. Isolation, sequence analysis and sequence assembly of tryptic peptides and cyanogen-bromide fragments.

The lac repressor from Escherichia coli, composed of four identical subunits with a molecular weight of 37160, was carboxymethylated and fragmented by tryptic digestion and cyanogen bromide treatment. Using ion-exchange chromatography, gel filtration and preparative thin-layer electrophoresis and chromatography 29 of the 30 tryptic peptides were isolated in pure form. Direct Edman degradation and the dansyl-Edman technique were used to determine the sequence of the small tryptic peptides. Special emphasis was put on the sequence determination of the six large tryptic fragments which together account for 177 residues, corresponding to 51% of the repressor subunit with its 347 residues. The large tryptic fragments were analyzed after fragmentation with chymotrypsin, thermolysin and dipeptidyl aminopeptidase I. Thus the sequence of all 30 tryptic peptides could be deduced. The complete sequences of all cyanogen bromide fragments were deduced from peptides obtained by tryptic, chymotryptic and thermolytic digestion of the individual fragments and by automated stepwise Edman degradation of lac repressor and of the large cyanogen bromide fragments. The order of the cyanogen bromide fragments was given by overlapping tryptic peptides. The resulting amino acid composition of the monomer is Asp15, Asn11, Thr18, Ser30, Glu14, Gln27, Pro13, Gly22, Ala44, Cys3, Val33, Met9, Ile17, Leu40, Tyr8, Phe4, Trp2, Lys11, His7, Arg19. The sequence of lac repressor shows no similarities with that of other proteins known to bind to DNA or RNA. The N-terminal 55 residues contain two homologous regions. This part of the sequence which is involved in lac operator binding might have been formed by gene duplication.

Amino Acid Sequence↗
PubMed1973

The amino-acid sequence of lac repressor.

The amino-acid sequence of lac repressor from Escherichia coli has been determined. The sequence contains 347 residues in the subunit single peptide chain. It shows no similarities with the sequences of histones or the known part of beta-galactosidase.

Amino Acid Sequence↗
PubMedDate not supplied

Flow, diffusion, and thermal convection in percolation clusters: NMR experiments and numerical FEM/FVM simulations.

Percolation objects were fabricated based on computer-generated, two- or three-dimensional templates. Random-site, semi-continuous swiss cheese, and semi-continuous inverse swiss-cheese percolation models above the percolation threshold were considered. The water-filled pore space was investigated by NMR imaging and, in the presence of a pressure gradient, NMR velocity mapping. The fractal dimension, the correlation length, and the percolation probability were evaluated both from the computer-generated templates and the corresponding NMR spin density maps. Based on velocity maps, the percolation backbones were determined. The fractal dimension of the backbones turned out to be smaller than that of the complete cluster. As a further relation of interest, the volume-averaged velocity was calculated as a function of the probe volume radius. In a certain scaling window, the resulting dependence can be represented by a power law the exponent of which was not yet considered in the theoretical literature. The experimental results favorably compare to computer simulations based on the finite-element method (FEM) or the finite-volume method (FVM). Percolation theory suggests a relationship between the anomalous diffusion exponent and the fractal dimension of the cluster, i.e., between a dynamic and a structural parameter. We examined interdiffusion between two compartments initially filled with H2O and D2O, respectively, by proton imaging. The results confirm the theoretical expectation. As a third transport mechanism, thermal convection in percolation clusters of different porosities was studied with the aid of NMR velocity mapping. The velocity distribution is related to the convection roll size distribution. Corresponding histograms consist of a power law part representing localized rolls, and a high-velocity cut-off for cluster-spanning rolls. The maximum velocity as a function of the porosity clearly visualizes the percolation transition.

Computer Simulation↗