PubMed Health⌕ Search

Biomedical subjects

J Lasch

Publications and source records attributed to J Lasch.

At least 55 records · Page 3Linked to original sources
PubMed1987

Penetration kinetics of liposomal hydrocortisone in human skin.

The applicability of liposomal hydrocortisone (HC) as a selective drug delivery system for cutaneous administration of glucocorticoids has been studied. With the liposomal form, a considerably better concentration-time profile was obtained in the individual layers of human skin than with the corresponding HC ointment. The pronounced carrier ability of liposomes for HC holds promise for an increase in its therapeutic efficacy, thus reducing unwanted side effects of the topical glucocorticoid therapy.

Administration, Topical↗
PubMed1987

[Kinetics of membrane-bound aldehyde dehydrogenase from Acinetobacter calcoaceticus].

In recent investigations we were able to demonstrate that the NADP-dependent aldehyde dehydrogenase of Acinetobacter calcoaceticus is an inducible enzyme localized in intracytoplasmic membranes limiting alkane inclusions. Long-chain aliphatic hydrocarbons and alkanols are inducers of the enzyme. It was purified by us and now kinetically characterized using the enzyme-micelle form, which contains bacterial phospholipids and a detergent (sodium cholate), too. The pH optimum of aldehyde dehydrogenase was determined to be at pH 10. The enzyme showed substrate inhibition (by aldehyde excess). The Ks and Km values of the leading substrate NADP+ were found to be 8.6 X 10(-5) and 10.3 X 10(-5)M independent of the chain-length of the aldehydes. The Km values of the aldehydes decreased depending on increasing chain-length (butanal: 1.6 X 10(-3), decanal: 1.5 X 10(-6)M). The Ki values (for inhibition by aldehyde excess) showed a similar behaviour (butanal: 7.5 X 10(-3), decanal: 3.5 X 10(-5)M) as well as the optimal aldehyde concentrations inducing the "maximal" reaction velocity (butanal: 5mM, decanal: 6 microM). The number of inhibiting aldehyde molecules per enzyme-substrate complex was determined to be n = 1. NADPH showed product inhibition kinetics (Ki(NADPH) = 2.2 X 10(-4)M), fatty acids did not. We were unable to measure a reverse reaction. The following ions and organic compounds were non-competitive inhibitors of the enzyme: Sn2+, Fe2+, Cu2+, BO3(3-), CN-, EDTA, o-phenanthroline, p-chloromercuri-benzoate, mercaptoethanol, phenylmethylsulfonyl fluoride, and diisopropylfluorophosphate; iodoacetate did not influence enzyme activity. Chloral hydrate was a competitive inhibitor of the aldehydes. Ethyl butyrate activates the enzyme, dependent on the chain-length of the aldehyde substrates.

Acinetobacter↗
PubMed1986

Liposome-bound cortisol: a new approach to cutaneous therapy.

Preparation and applicability of liposome-bound cortisol as a drug delivery system for cutaneous administration of glucocorticoids have been investigated. With the liposomal drug a very much improved concentration-time profile was obtained in the different layers of human skin when compared with conventional cortisol in the ointment. The pronounced carrier ability of liposomes for cortisol in the skin holds promise for an increase in its therapeutic efficiency, while at the same time reducing unwanted systemic side effects of the topical glucocorticoid therapy.

Administration, Topical↗
PubMed1986

Determination of antibodies to rubella virus with the disperse dye immunoassay (DIA) in comparison with an enzyme-linked immunosorbent assay (ELISA).

A disperse dye immunoassay (DIA) using Fantagen-dye sol particles as label was developed for the measurement of rubella antibodies in human serum specimen. The DIA has a sensitivity comparable to the hemagglutination-inhibition (HI) test, whereas the detection limit for a similar ELISA-system developed in parallel is lower by a factor of about two orders of magnitude. The results of testing 34 random serum specimens with the 3 different methods showed a significant correlation (v = 0.73 for DIA vs. ELISA). Titer rises in 10 paired sera (acute/convalescent) estimated with the DIA- and ELISA-methods were in good agreement with H1-results. Only two of the 10 pairs differed in titer rise by no more than one dilution step.

Antibodies, Viral↗
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

Suitability of Fantagen dyes and tablet blisters for the disperse dye immunoassay.

Among the numerous labels employed in immunoassays dye sol particles have been introduced but recently. This report deals with a modification of the disperse dye immunoassay (DIA). It is shown that Fantagen dyes to which antibodies were adsorbed physically and tablet blisters as solid phase give satisfactory results with the model antigens alpha 2-macroglobulin and the group specific component of human plasma.

Alpha-Globulins↗
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↗
PubMed1980

Catalytic properties and electrostatic potential of charged immobilized enzyme derivatives. Pyruvate decarboxylase attached to cationic polystyrene beads of different charge densities.

Pyruvate decarboxylase has been covalently attached to positively charged macroporous polystyrene resins. The changes in the functional behaviour of the enzyme resulting from the electrostatic interaction of the cationic carrier polymer and the anionic substrate have been studied as function of the fixed charge concentration of the carrier. The findings confirm the connection of two widely used theoretical expressions relating electrostatic parameters with Michaelis constants.

Carboxy-Lyases↗
PubMed1980

Growth regulation of lens epithelial cells. Chemically-modified sepharose as a suitable substratum for studying cell-substratum interactions.

Suitable substrata for studying cell-substratum interactions were prepared by melting of unsubstituted and substituted agarose beads (Sepharose). The reductive alkylation procedure proved to be useful in introducing various ligands into the gel matrix. The resulting bonds remained stable during sterilisation and melting. The introduction of charges into the gel matrix facilitated cell adhesion to the substratum. But only positively-charged agarose substrata were as effective as glass surfaces in supporting cell attachment. The correlation found between cell attachment and the stimulation of DNA synthesis demonstrates that lens epithelial cells are strongly anchorage dependent.

Animals↗
PubMed1980

[Relationship between catalytic properties, fixed charge concentration and electrostatic potential of polyelectrolyte-bound enzymes].

An equation for the calculation of the electrostatic potentials of polyelectrolyte-enzyme supports from electrostatic parameters has been derived by relating two different theories which describe the catalytic behaviour of polyelectrolyte-bound enzymes. The electrostatic potentials of polyionic supports have been determined by use of experimental results, on the one hand, from the fixed charge concentration and the ionic strength, on the other hand, from pH- and Km-shifts of immobilized enzymes. The accordance of potentials calculated from electrostatic and kinetic parameters confirms the macroscopic carrier-enzyme model.

Amylases↗
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↗