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W Demmer

Publications and source records attributed to W Demmer.

8 recordsLinked to original sources
PubMed1999

Large-scale membrane adsorbers.

A new large-scale membrane adsorber system for rapid separation of biomolecules based on a hollow cylindrical module geometry in unitized construction and combined parallel and serial connection of modules is presented. The effectiveness of the concept is demonstrated by breakthrough curves on a 21-m2 pilot plant with hemoglobin as a model substance. Scale-up to the order of 100 m2 and above is easily performed by combining modules in parallel for increasing capacity, and in series for optimizing performance. An estimation of productivity based on these data is presented. Preliminary results of separations by linear salt gradient elution are also given.

Adsorption↗
PubMed1986

A putative opioid-peptide processing activity in enriched Golgi fraction from rat brain.

A Golgi enriched fraction from rat brain was prepared. The preparation has no carboxypeptidase activity and is not contaminated with cytosol, mitochondria and lysosomes as judged by marker enzyme activities for these constituents. Associated with the Golgi membranes a putative opioid peptide processing activity was demonstrated, which acts on Dynorphin 1-13, alpha- and beta-Neoendorphin. The enzyme cleaves the bond between the paired basic residues, releasing Leucine-enkephalin-Arg6. The activity has a pH-optimum around 9 and is inhibited by serine-protease inhibitors. Intracellular location and substrate specificity suggest that this endopeptidase activity may be involved in proenkephalin processing.

Amino Acid Sequence↗
PubMed1985

Carboxypeptidase activity in synaptic vesicles isolated from striatum and cortex of calf brain.

A carboxypeptidase activity has been found in synaptic vesicles (secretory granules) isolated from the cortex and striatum of calf brain which removes amino acids from the carboxy terminus of enkephalin-containing (EC) peptides. The formed enkephalin molecules are not further degraded by this enzyme activity. The preparations were found to be free of cytoplasmic and lysosomal constituents as determined by marker enzyme activities. The vesicle preparations of both cortex and striatum showed differences in the degradation velocities of the various EC peptides depending on size and charge of the amino acid present at the carboxy terminus. The pH optimum of the release of Met-enkephalin from Met-enkephalin-Arg6 has been shown to be between pH 5 and 6. The enzyme activity is inhibited by thiol-blocking agents such as p-hydroxymercuribenzoate and copper ions, but only slightly by metal-chelating agents.

Animals↗
PubMed1983

A dipeptidyl carboxypeptidase in brain synaptic membranes active in the metabolism of enkephalin containing peptides.

A dipeptidyl carboxypeptidase activity has been localized in synaptic plasma membranes which have been prepared from isolated rat brain cortical synaptosomes. The specificity of this proteolytic activity towards various synthetic and biological active peptides is compared to the peptidase activities of intact synaptosomes. In contrast to the synaptosomal peptidases which are capable of cleaving all peptide bonds of Met-enkephalin-Arg6-Phe7 the peptidase activity associated with the synaptic plasma membrane exclusively hydrolyses a dipeptide from the carboxyl terminus of all hepta- and hexapeptides tested. The fact that this dipeptidyl carboxypeptidase does not cleave the Gly3-Phe4 peptide bond of Met-enkephalin suggests that this enzyme is different from "enkephalinase". The synaptic membrane dipeptidyl carboxypeptidase is inhibited by metal chelating agents and thiols but is not affected by compounds known to inhibit serine proteases, thermolysin and "enkephalinase".

Amino Acid Sequence↗
PubMed1983

Processing and degradation of met-enkephalin by peptidases associated with rat brain cortical synaptosomes.

The generation of met-enkephalin (Tyr1-Gly2-Gly3-Phe4-Met5) from met-enkephalin-Arg6-Phe7 and subsequent degradation of the liberated peptides to the free amino acids by rat brain cortical synaptosomes in vitro was demonstrated by HPLC and amino acid analyses. Kinetic measurements of the individual steps of met-enkephalin processing and degradation upon incubation with synaptosomes revealed the following sequence of cleavage: 1. Hydrolysis of the Met5-Arg6 peptide bond, generating met-enkephalin and the dipeptide Arg-Phe. Captopril and EDTA inhibit this reaction. 2. Hydrolysis of the Tyr1-Gly2 peptide bond, generating Tyr and a tetrapeptide. Puromycin (ID50 = 5 X 10(-5) M) and parahydroxymercuribenzoate (ID50 = 5 X 10(-4) M) inhibit this reaction. 3. Hydrolysis of the Gly3-Phe4 peptide bond. Parahydroxymercuribenzoate (ID50 = 5 X 10(-4) M) inhibits this reaction completely. 1 mmol liter-1 Puromycin does not inhibit this reaction. 4. Hydrolysis of the Phe4-Met5 peptide bond. 5. Hydrolysis of the Gly2-Gly3 peptide bond. The pH optimum of all cleavage reactions was found to be around 7.8.

Amino Acids↗
PubMed1983

Some properties of aminopeptidase associated with rat brain cortical synaptosomes.

To understand the breakdown of peptides in the brain, we studied the aminopeptidase associated with synaptosome particles. A continuous spectrophotometric assay in stirred cuvettes was used to follow the kinetics of inactivation by EDTA and by diethyl pyrocarbonate. The sensitivity of the enzyme towards puromycin and leucine hydroxamate was also determined. The results are consistent with the presence of a single species of aminopeptidase in freshly prepared synaptosome. This enzyme is capable of degrading Met-enkephalin in vitro and is distinct from microsomal leucine aminopeptidase. Storage of synaptosomes by freezing and subsequent thawing changed some properties of the enzyme and partially solubilized the enzyme. These studies suggest that there are advantages in studying the enzyme in its native particle-bound state.

Aminopeptidases↗
PubMed1982

Inhibition of leucine aminopeptidase by amino acid hydroxamates.

Amino acid hydroxamates are strong competitive inhibitors of leucine aminopeptidase from porcine kidney. The side chain specificity for inhibition correlates well with substrate specificity. L-Leucine hydroxamate (Ki = 14 microM) protects the enzyme from inactivation by EDTA and is presumed to be a bidentate ligand of the zinc at the active site. A substituted beta-mercaptoketone which may bind in a similar way is also a potent inhibitor (Ki = approximately 1 microM). The binding of these inhibitors suggests a mechanism for this enzyme in which a zinc-bound hydroxide ion participates in concerted proton-transfer processes, while the coordination and charge field at the zinc atom remain unchanged.

Amino Acids↗