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J Lasch

Publications and source records attributed to J Lasch.

At least 73 records · Page 4Linked to original sources
PubMed1976

Thermal stability of immobilized enzymes circular dichroism, fluorescence and kinetic measurements of alpha-chymotrypsin attached to soluble carriers.

The temperature-induced unfolding of alpha-chymotrypsin and of chymotrypsin covalently bound to two soluble transparent carriers, dextran and a copolymer of maleic acid anhydride and acrylic acid, has been studied by tryptophan fluorescence emission, circular dichroic and kinetic measurements. It has been shown that the structural and functional properties of the enzyme when bound to the anionic copolymer are strongly influenced by electrostatic interactions. A number of reference experiments with anionic polyelectrolytes and the hydrogenated monomers of the copolymer suggest that these changes are brought about by the cooperative ion pair formation between protein and polyanionic matrix.

Acrylates↗
PubMed1976

[Spectroscopic investigatons on the structural thermal stability of leucine aminopeptidase. ESR, CD and fluorescence studies].

The thermal behaviour of leucine aminopeptidase (LAP, EC: 3.4.11.1) from bovine eye lens has been investigated in the temperature region 20--70 degrees C by spin-labelling of SH-groups (ESR), by CD and by fluorescence of tryptophane residues. Enzymatic activity of LAP was compared with spectroscopic data in this temperature region. From 20-60 degrees C the structural parts (alpha, beta, random coil) estimated from CD spectra remain unchanged. Within 20-55 degrees C no irreversible exposure of tryptophane residues takes place. In both types of spin-labelled LAP the strong immobilizing environment of the label retains its highly ordered structure up to 55 degrees C. Reversible changes of mobility and polarity of the environment of the label induced by temperature within 20-50 degrees C do not reduce the enzymatic activity and are regarded as local loosening of ordered structure. At 65 degrees C strong precipitation occurs. From 55 degrees C to 65 degrees C tryptophane residues are irreversibly exposed. The highly ordered environment of the label is destroyed about 55 degrees C, and a considerable amount of spin label molecules is reduced at the NO group by exposed SH groups. The above mentioned local loosening of structure becomes irreversible at 60 degrees C. The environment of both labels dominating above 60 degrees C is highly mobile and strongly polar and represents an extensively unfolded conformation. Until 60 degrees C no essential disordering of protein structure leading to a decrease of enzymatic activity occurs. Above 60 degrees C a sharp breakdown of ordered structures takes place, which is accompanied by a strong diminution of enzymatic activity.

Animals↗
PubMed1976

[CHEMICAL OSCILLATIONS IN THE ONE-ENZYME REACTOR].

The theory of nonlinear oscillations was applied to a special dynamic system, the continuous stirred tank enzyme reactor (CSTR), in order to find out the enzyme mechanisms which may lead to the appearence of chemical oscillations in the one-enzyme reactors. In the main, the isothermic reactor without diffusion limitation was studied. The possibilities of a mathematical analysis of periodic processes in single catalyst beads and one-enzyme column reactors with diffusion limitation are briefly discussed.

Diffusion↗
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

Fluorescence and chemical reactivity as empirical indices of matrix-induced alterations in immobilized enzymes.

The fluorescence emission and chemical reactivity of soluble and Sepharose-bound leucine aminopeptidase and carboxypeptidase A were investigated and the results compared. Both natural fluorescence and the fluorescence of fluorescein-labeled enzymes were utilized. The front-surface viewing technique enables us to measure the apparent fluorescence quantum yields and the rotational relaxation times of fluorescent groups within native unbound and carrier-fixed enzymes. The chemical reactivity was probed with Ellman's reagent and iodoacetic acid. Both types of methods were found to be useful in detection and quantitation of matrix-induced alterations in immobilized enzymes.

Carboxypeptidases↗
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↗