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Biomedical subjects

B Hock

Publications and source records attributed to B Hock.

53 records · Page 3Linked to original sources
PubMed1992

Self-tonometry: technical aspects of calibration and clinical application.

Self-tonometry could be established as an important diagnostic tool in the early diagnosis and follow-up of glaucoma provided that a self-tonometer is precise, safe and easy to use. Furthermore, it has to comply with the legal standards for tonometer calibration. A new software-controlled detection system for the self-tonometer permits the evaluation of external factors during the measurement which influence the precision of the tonometric readings. The updated version of the self-tonometer (ST) was compared to the Draeger hand-held applanation tonometer (HAT) in a clinical study with 82 patients (151 eyes). The results show a regression line characterized by a slope of 0.99, an y interception of 1.41, a correlation coefficient of 0.96 and a standard deviation for the ST readings of +/- 1.78 mmHg. Self-tonometry improves the IOP monitoring as well as patient compliance and therefore is a potential diagnostic tool in the management of glaucoma.

Calibration↗
PubMed1992

Development of a piezoelectric immunosensor for the detection of enterobacteria.

A piezoelectric crystal immunosensor has been developed for the detection of enterobacteria in drinking water using antibodies against the enterobacterial common antigen. Applying an anti-enterobacterial antibody layer via protein A immobilization onto a 10-MHz crystal, a response is observed for 10(6) to 10(9) cells ml-1 of Escherichia coli K12, and for various other antigens of the Enterobacteriaceae family.

Antibodies, Monoclonal↗
PubMed1992

A piezoelectric immunobiosensor for atrazine in drinking water.

A piezoelectric crystal immunobiosensor has been developed for the assay of atrazine herbicides in drinking water. Determinations from 0.03-100 micrograms l-1 (parts per billion) of atrazine can be made with a relative SD of about +/- 8%. Atrazine antibodies (polyclonal from sheep) are layered onto the gold electrode of 10 MHz piezoelectric crystals, which are precoated with protein A. The sensor is reversible, being reusable for about eight or nine assays.

Atrazine↗
PubMed1991

Clinostatic rotation decreases crossover frequencies in the fungus Sordaria macrospora Auersw.

Two-factor crosses between the non-allelic spore colour mutants r2 and lu of the fungus Sordaria macrospora were used to investigate the effect of clinostatic rotation (= simulated weightlessness) on crossover frequencies. The experiment was carried out with different rotary directions at a rotary rate of 4 rpm. Second-division segregations of the gene lu, which result from crossover between the gene locus and centromere, are significantly smaller in the clinostat experiments than in the static controls. No differences were found between the two rotary directions. A similar influence of clinostatic rotation was not observed for the gene r2 which in contrast to the lu locus is located very close to the centromere. The suitability of this approach for the investigation of the effect of space flight conditions on cytogenetic processes is pointed out.

Chromosome Mapping↗
PubMed1990

Influence of ozone and acid mist on the contents of gibberellic acid (GA(3)) in spruce needles (Picea abies) (L.) Karst.

The phytohormone GA(3) in needles from 4-year-old Norway spruce trees was analyzed after treatment with ozone and acid mist in environmental chambers under controlled conditions. GA(3) was extracted with methanol from the lyophilized material. Subsequent purification steps included the use of polyvinylpyrollidone (PVP), cartridge reversed-phase purification, ethylacetate extraction and HPLC. The GA(3) was determined in the methylated form by means of a highly specific and sensitive enzyme immunoassay. Higher GA(3) contents were detected in young needles (year 1987) as compared to older ones (year 1986). However, no statistically significant differences were found in the GA(3) levels between the controls and the needles of trees which were treated with increased levels of ozone and acidic mist.

Journal Article↗
PubMed1987

Toxic components of motor vehicle emissions for the spruce Picea abies.

Six-year-old Norway spruce trees were exposed for 30 min under standardised conditions to the exhaust from an Otto engine running on lead-free petrol. Gas-exchange measurements in an open system using an infrared gas analyser showed a sudden, severe drop in CO(2) assimilation and transpiration rates. By using filters which absorbed different fractions of the exhaust it could be demonstrated that the toxic effects can be attributed to the NO(x) fraction.

Journal Article↗
PubMed1987

Atmospheric transport of atrazine: a simple device for its detection.

Thin-layer chromatography plates were exposed at three different locations in Bavaria for 3-week periods during the growing season of maize. The adsorption of traces of atrazine was detected by thin-layer chromatography, GC-MS, and by an enzyme immunoassay. It was restricted to the sowing season, which coincides with the application of atrazine. The herbicide could not be detected after this time. The simplicity of the adsorption device, combined with a serological assay, render this procedure suitable for detecting airborne organic pollutants.

Journal Article↗
PubMed1982

Organelle-bound malate dehydrogenase isoenzymes are synthesized as higher molecular weight precursors.

Biosynthesis of malate dehydrogenase isoenzymes was studied in cotyledons of watermelons (Citrullus vulgaris Schrad., var. Stone Mountain). The glyoxysomal and mitochondrial isoenzymes are synthesized as higher molecular weight precursors which can be immunoprecipitated by mono-specific antibodies from the products of in vitro translation in reticulocyte lysates programed with cotyledonary mRNA and with the same size from enzyme extracts of pulse-labeled cotyledons. During translocation from the cytosol into the organelles, processing takes place. An 8 kilodalton extra sequence is cleaved from the glyoxysomal precursor and a 3.3 kilodalton extra sequence from the mitochondrial precursor producing the native subunits of 33 and 38 kilodaltons, respectively. The data support a post-translational translocation of the organelle-destined malate dehydrogenase isoenzymes. The in vitro translation of the cytosolic malate dehydrogenase I yields a product which has the same molecular weight as the subunit of the native isoenzyme (39.5 kilodaltons).

Journal Article↗
PubMed1982

Fluorescence immunohistochemical localization of malate dehydrogenase isoenzymes in watermelon cotyledons : a developmental study of glyoxysomes and mitochondria.

Monospecific antibodies to glyoxysomal, mitochondrial, and cytosolic I malate dehydrogenase were used for the fluorescence immunohistochemical localization of these isoenzymes in dark-grown watermelon (Citrullus vulgaris Schrad.) cotyledons. It was demonstrated that, with cell organelles isolated by sucrose density gradient centrifugation, antibodies to glyoxysomal malate dehydrogenase were specific markers for glyoxysomes, and similarly, antibodies to mitochondrial malate dehydrogenase were markers for mitochondria. The time course of the glyoxysomal malate dehydrogenase appearance and decline was not synchronous for the individual tissues and differed completely from that of the mitochondria. The cytosolic malate dehydrogenase I was confined to restricted regions of the lower epidermis. The activity which was definitively localized outside the cell organelles decreased during the first days of germination.

Journal Article↗
PubMed1982

Cell-free synthesis of watermelon glyoxysomal malate dehydrogenase: a comparison with the mitochondrial isoenzyme.

Cotyledons of dark-grown watermelon seedlings contain during the first period of germination, 4 and later 5 MDH isoenzymes. Whereas isoenzymes I, II, and IV belong to the cytosol, isoenzyme III is confined to the mitochondria (mMDH) and isoenzyme V to the glyoxysomes (gMDH). The organelle-bound MDHs were purified to homogeneity and characterized. They are remarkably similar with respect to their kinetic properties, but differ widely in other characteristics, e.g. MW, IEP, thermostability, and serological properties. Both isoenzymes are synthesized de novo during germination by cytoplasmic ribosomes. In a reticulocyte cell-free system programmed by watermelon poly (A+) RNA, gMDH and mMDH are synthesized as larger precursors as compared to the authentic polypeptide chains, with an extra sequence of ca. 8.0 kilodaltons in the case of gMDH and ca. 3.3 kilodaltons with mMDH. The processing of the gMDH precursor by an enriched organelle fraction in not complete. If the post-translational incorporation of the in vitro product into the organelles is followed by proteinase treatment that completely hydrolyzes noncompartmentalized gMDH, the authentic product is obtained. A model for the transport mechanism is given.

Cell-Free System↗
PubMed1976

Separation of malate dehydrogenase isoenzymes by affinity chromatography on 5'-AMP-Sepharose.

The mitochondrial and glyoxysomal isoenzymes of malate dehydrogenase (EC 1.1.1.27) from watermelon cotyledons and the mitochondrial isoenzyme from pig heart adsorbed reversibly to 5'-AMP-Sepharose. They were specifically eluted with low concentrations of NADH rather than by NAD. In contrast, the cytoplasmic isoenzymes showed no affinity to the matrix-bound ligand. These binding properties are discussed in terms of structural and regulatory differences of the particulate and soluble malate dehydrogenase isoenzymes. Affinity chromatography on 5'-AMP-Sepharose significantly improved the purification of the particulate malate dehydrogenase isoenzymes with respect to homogeneity, yield, and the number of purification steps. In the case of the glyoxysomal isoenzyme it was the essential procedure to obtain complete purification of the enzyme.

Adenosine Monophosphate↗
PubMedDate not supplied

Long-term monitoring of atrazine contamination in soil by ELISA.

An enzyme-linked immunoassay (ELISA) was used for screening atrazine residues in soil. Samples were annually collected in Southern Germany between 1993 and 1998. An average of 419.5 samples was analyzed per year amounting to 2517 samples. The fraction of positive samples defined by atrazine concentrations >100 microg/kg soil decreased successively from 8% (corresponding to 33 samples) in 1993 to 0.6% (corresponding to 2 samples) in 1998. All positive samples and a selection of negative samples were subsequently validated by HPLC. Comparison of ELISA and HPLC data yielded correlation coefficient values of r = 0.958-0.981 (n = 18-47), except for 1995 when only a correlation of r = 0.864 (n = 18) was obtained. Four samples were overestimated and another 4 were underestimated with respect to the atrazine threshold value of 100 microg/kg soil as revealed by HPLC validation. Thus, 99.68% of 2,517 analyzed samples were correctly evaluated. The precision and reproducibility of the ELISA were adequate for a prescreening tool. The low cost per sample and the high sample throughput are not yet achievable by conventional analytical methods. The described combination of ELISA and HPLC has the potential to take advantage of both methods and to restrict determination errors to a minimum.

Atrazine↗