220-Rn retention in mouse bone

Conclusions The experiment has shown that about half of the²⁰⁰Rn produced from²²⁴Ra in mouse bone escapes before decay in the period up to 8 days following injection. It is expected that the radiation dose delivered to structures within bone will be reduced in consequence.     

Reconstitution of the tonoplast amino-acid carrier into liposomes

The tonoplast amino-acid transporter of barley (Hordeum vulgare L.) mesophyll cells was functionally reconstituted by incorporating solubilized tonoplast membranes, vacuoplast membranes or tonoplast-enriched microsomal vesicles into phosphatidylcholine liposomes. (i) Time-, concentration- and ATP-dependence of amino-acid uptake were similar to results with isolated vacuoles. Although the orientation of incorporation could not be controlled, the results indicate that the transporter functions as a uniport system which allows regulated equilibration by diffusion between the cytosolic and vacuolar amino-acid pools. (ii) The ATP-modulated amino-acid carrier was also successfully reconstituted from barley epidermal protoplasts and Valerianella or Tulipa vacuoplasts, indicating its general occurrence. (iii) Fractionation of solubilized tonoplasts by size-exclusion chromatography followed by reconstitution of the fractions for glutamine transport gave two activity peaks: the first eluted in the region of high-molecular-mass vesicles and the second at a size of 300 kDa for the Triton-protein micelle.Abbreviation SDS-PAGE sodium dodecyl sulfate-polyacryl-amide gel electrophoresis This work was part of our research efforts within the Sonderforschungsbereich 176 of the University. We gratefully acknowledge experimental support by Marion Betz and valuable discussions with Professors U. Heber and U.-I. Flügge and Dr. Armin Gross (University of Würzburg) and Dr. E. Martinoia (ETH, Zürich, Switzerland).     

An automatic method for determination of urinary 3-methylhistidine: normal values.

A system for automatic analysis of urinary 3-methylhistidine is described, applying ion-exchange chromatography and using an automatic sample injector, a motoric selector valve, and a diode programmer, which controls the analytical system. The method permits a sampling rate of 22 samples/day. 3-Methylhistidine was completely separated from histidine in 37 min whereas 1-methylhistidine was eluted together with ammonia. The 3-methylhistidine concentration was linear up to 150 nmol/ml and no appreciable sample interaction was found at automatic sequential runs. The error, in a single determination based on duplicate samples, was 4.61% and, in duplicated determinations, 3.26%. The mean urinary 3-methylhistidine output was 299.4 ± 23.8 μmol/day in 12 healthy females and 545.5 ± 35.2 μmol/day in 12 healthy males. The 3-methylhistidine excretion was significantly higher in males than in females, when expressed as the absolute daily output or as the estimated ratio to body weight, body surface area, or creatinine.     

Dihydroorotate dehydrogenase from Saccharomyces cerevisiae: spectroscopic investigations with the recombinant enzyme throw light on catalytic properties and metabolism of fumarate analogues

In all organisms the fourth catalytic step of the pyrimidine biosynthesis is driven by the flavoenzyme dihydroorotate dehydrogenase (DHODH, EC 1.3.99.11). Cytosolic DHODH of the established model organism Saccharomyces cerevisiae catalyses the oxidation of dihydroorotate to orotate and the reduction of fumarate to succinate. Here, we investigate the structure and mechanism of DHODH from S. cerevisiae and show that the recombinant ScDHODH exists as a homodimeric enzyme in vitro. Inhibition of ScDHODH by the reaction product was observed and kinetic studies disclosed affinity for orotate (K(ic)=7.7 microM; K(ic) is the competitive inhibition constant). The binding constant for orotate was measured through comparison of UV-visible spectra of the bound and unbound recombinant enzyme. The midpoint reduction potential of DHODH-bound flavine mononucleotide determined from analysis of spectral changes was -242 mV (vs. NHE) under anaerobic conditions. A search for alternative electron acceptors revealed that homologues such as mesaconate can be used as electron acceptors.