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Biomedical subjects

R Koelsch

Publications and source records attributed to R Koelsch.

At least 19 recordsLinked to original sources
PubMed1989

[Interactions of detergents with phospholipid bilayers at sublytic concentrations--partition or binding?].

Using the bubble pressure method the interaction of liposomes with detergents at sublytic concentrations was studied. The results are discussed in terms of a partition or binding model. The findings support an equilibrium partition of the surfactant between the aquous and lipid phase. For some detergents, however, concentration dependent partition coefficients were found.

Chemical Phenomena↗
PubMed1988

Enzymic properties of intestinal aminopeptidase P: a new continuous assay.

A continuous photometric assay of aminopeptidase P activity was developed which is based on a coupled enzymic assay with the substrate Gly-Pro-Pro-pNA and DPP IV as auxiliary enzyme. This assay was used to evaluate the kinetic parameters and inhibitory profile of intestinal brush border aminopeptidase P.

Amino Acid Sequence↗
PubMed1986

Is the proline-specific aminopeptidase P of the intestinal brush border an integral membrane enzyme?

It has been found that the microvillous membrane of rat enterocytes contains an aminopeptidase P which is one of the few enzymes capable to hydrolyze the peptide imido bond on the N-terminal side of proline residues. The enzyme was enriched 9-fold in chromatographically purified brush border membrane vesicles of the small intestine. Various extraction procedures and proteinase treatments yielded strong evidence that it is an integral part of the membrane without a stalked hydrophilic head exposed to the outer surface. It was solubilized by detergent and further enriched by ion exchange chromatography up to 73-fold.

Aminopeptidases↗
PubMed1984

Incorporation of chemically modified (hydrophobized) ferritin in liposomal membranes: electron microscopic studies.

The assembly of electron dense ferritin modified by acylation with steaorylchloride into small and large egg lecithin vesicles is reported. From electron micrographs conclusions are drawn: on the mode of ferritin incorporation in the lipid bilayer: Small liposomes seem to be only in superficial contact with the modified protein shell of the ferritin molecule whereas in the larger lipid vesicle type the incorporation is more integral.

Animals↗
PubMed1983

A method to measure critical detergent parameters. Preparation of liposomes.

A simple physical method to determine the monomer concentration of detergents below as well as above the critical micelle concentration based on the bubble-pressure measurement is described. Aggregated surfactant molecules (micelles) and phospholipid vesicles if present in the sample will not disturb the measurements. Three applications of the method relevant to the preparation of liposomes are shown: (i) measurements of critical micelle concentrations, (ii) evaluation of the affinity constant of the interaction of detergents with liposomal membranes, and (iii) monitoring of residual detergent in liposome preparations during dialysis or after gel chromatography of mixed micelle-derived liposomes. It was found that the efficiency of detergents to produce liposomes during their removal depends on their critical micelle concentrations as well as on their affinity to liposomal membranes.

Cholic Acid↗
PubMed1982

Auto-oxidation-induced fusion of lipid vesicles.

Spontaneous size changes of small unilamellar vesicles with initial mean diameters of 25 nm measured by quasi-elastic light scattering (QELS) and electron microscopy are reported. After the size conversion the vesicles have mean diameters of about 70 nm and are of the unilamellar and multilamellar type. The fact that auto-oxidation initiates this process is established by the comparison of the results for vesicles which differ only in the degree of auto-oxidation. The role of phosphatidylcholine hydroperoxides as fusogens is discussed.

Light↗
PubMed1981

Incorporation of chemically modified proteins into liposomes.

Enzymes, not anchored into bilayers of membranes like trypsin, alpha-chymotrypsin, and carboxypeptidase A are chemically modified by acylation with fatty acids chlorides. This treatment renders these proteins hydrophobic so that they can combine with the phospholipid membrane of liposomes. This report deals with the incorporation of modified enzymes into liposomes prepared by different methods.

Acylation↗
PubMed1978

Enzyme leakage and multipoint attachment of agarose-bound enzyme preparations.

The solvolytic detachment of leucine aminopeptidase from Sepharose-enzyme conjugates with multiple and single anchoring bonds has been studied under a variety of conditions by radiochemical and enzymological methods. The release of the single-point-fixed conjugate could be described by a leakage function, derived previously, yielding the first-order rate constant of the cleavage of the enzyme-matrix bond. The nucleophile hydroxylamine increased the detachment rate considerably. The release of the immobilized enzyme was incomplete in all experiments even after prolonged times. The enzyme leakage from multipoint-attached conjugates was still high enough to prohibit a long-term use of such preparations in routine work at room temperature.

Amino Acids↗
PubMed1977

Protein degradation in rat liver cells.

The intracellular protein catabolism in isolated hepatocytes is inhibited by pepstatin and particularly by leupeptin in the presence of liposomes. Leupeptin has an inhibitory action both in the absence and in the presence of liposomes (nearly 40%).

Animals↗
PubMed1976

[Protein hydrolysis by immobilized enzymes].

The enzymic hydrolysis of some proteins (insulin-B-chain-S-sulfonate, S-aminoethylated lysozyme, bovine serum albumin) by immobilized peptidolytic enzymes is reported. Sepharose-bound pronase, trypsin and a protease from Thermoactinomyces sp. (MP), the latter both cross linked by glutaric dialdehyde and an exopeptidase mixture containing Sepharose-bound leucine aminopeptidase, carboxypeptidase A and a crude preparation of prolidase were used. After enzymic hydrolysis nearly all amino acids, except proline, were recovered in a 100% yield compared to the value of an acid reference hydrolysate. Tryptophan and methionine, which are partially destroyed by acid hydrolysis in the presence of oxygen could be recovered completely.

Aminopeptidases↗
PubMed1975

Studies of the distribution of proteins bound to CNBr-activated Sepharose 6B at the electron-microscopic level.

Proteins were covalently attached to Sepharose by the CNBr method. Their distribution across the carrier beads was studied at the electron microscopic level. The approach has been to ferritinstain and to section the gel beads. Ferritin was either coupled directly to the polysaccharide backbone of the carrier or conjugated with pure rabbit anti-aminopeptidase in order to visualize covalently bound leucine aminopeptidase by the immunferritin technique. The results corroborate earlier fluorescence microscopic findings of a uniform protein distribution, provided that a number of conditions are fulfilled.

Binding Sites↗
PubMed1975

An inexpensive device for sample stirring in VSU Zeiss spectrophotometers. Its use for kinetic measurements and active site titrations with immobilized enzymes.

The construction of a simple and effective sample stirring device for commercial spectrophotometers and its use for continuous kinetic measurements and active site titrations with immobilized enzymes is described. Sepharose-bound leucine aminopeptidase and trypsin were selected as model enzymes to test the performance of the magnetic stirring equipment. Kinetic parameters of insolubilized leucine aminopeptidase using L-leucine p-nitroanilide as substrate and the catalytic site concentration of matris-bound trypsin using p-nitrophenyl p'-guanidinobenzoate as active site titrant could be evaluated without significant interference from the turbidity of the stirred Sepharose suspension. The problem of grinding of the support material could be overcome. Both unbound native and carrier-fixed enzyme may be reacted under identical conditions with similar convenience and sensitivity.

Animals↗