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Biomedical subjects

H Arwin

Publications and source records attributed to H Arwin.

11 recordsLinked to original sources
PubMed1987

Non-chromogenic peptide substrates for detection of enzymes by means of capacitance changes at metal electrodes.

A new type of substrate for enzyme detection has been developed. The substrate is non-chromogenic and is used in an assay method based on electrode adsorption. The rate of change in the electric capacitance of the electrode is monitored and taken as a measure of the substrate adsorption. Substrate adsorption is in turn proportional to substrate bulk concentration and thus subject to changes by enzymes. The new substrate introduces a new concept in enzyme detection: as it is non-chromogenic it may contain appropriate amino acids on both sides of the bond subject to enzymatic cleavage.

Electrochemistry↗
PubMed1985

A reflectance method for quantification of immunological reactions on surfaces.

A simple optical method for determination of thicknesses of organic layers on solid substrates is described. The method is based on the use of a substrate with a high refractive index, e.g., silicon, and reflection of light at an angle of incidence close to the pseudo-Brewster angle. Under these conditions, a reflectance minimum is obtained for light polarized in the plane of incidence. The presence of an organic layer on the surface will increase the reflectance, which is used to determine the thickness of the layer. The physical basis of the method is described briefly, and the application to immunology is demonstrated.

Antigen-Antibody Reactions↗
PubMed1983

The electrode adsorption method for determination of enzyme activity: a study of substrate requirements.

The electrode adsorption method for the determination of enzyme activity requires substrates that, besides having good kinetics constants for the enzyme, also show good adsorption/desorption kinetics to the electrode surface and adsorb in such a way that they change the double-layer capacitance of the electrode. A series of peptide substrates containing one to three aromatic groups has been synthesized. Our results show that the aromatic groups are of crucial importance for the capacitance change caused by the adsorbing/desorbing substrate. Thus, the tripeptide substrate, Bz-Phe(NO2)-Val-Arg-pNA, with three aromatic groups is superior to the other synthesized substrates containing only one or two aromatic groups. Our desorption experiments show that several factors determine the rate of capacitance increase observed when thrombin is added to a substrate solution in equilibrium with a substrate-covered electrode. The kinetic constants of the substrate determine how the substrate concentration in the solution decreases and, consequently, determine the spontaneous desorption measured as capacitance increase. Thrombin does not seem to split adsorbed substrate molecules but it adsorbs to the substrate-covered surface and in that way causes a capacitance decrease counteracting the change caused by desorption of substrate.

Adsorption↗
PubMed1982

Ellipsometric studies of film formation on tooth enamel and hydrophilic silicon surfaces.

The uptake of salivary substances onto hydrophilic negatively charged surfaces of silicon or onto enamel surfaces was studied in vitro with ellipsometry. There was a rapid initial uptake of substances followed by a slow but continuous uptake probably of other substances, which could be removed from saliva by absorption with a S. mutans serotype c strain. the kinetics for the uptake onto enamel and silicon surfaces and the thicknesses of the layers were similar. The combination of ellipsometry and silicon surfaces is suggested as a model for obtaining increased information on dental pellicle formation.

Chemical Phenomena↗
PubMed1979

The isoelectric point of thrombin and its behaviour compared to prothrombin at some solid surfaces.

We have shown that the isoelectric point of thrombin is high and that thrombin is a cation at the pH of blood. On the other hand, prothrombin has a low isoelectric point, being more anionic at the pH of blood. It was also found that thrombin adsorbs readily to surfaces, especially negatively charged surfaces, like behenic acid surfaces at pH 8.2. Furthermore, thrombin adsorbed onto behenic acid was active in the sense that it coagulated fibrinogen. The significance of the electric charge of the thrombin molecule in the mechanism of atherosclerosis is discussed.

Adsorption↗