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T S Hsu

Publications and source records attributed to T S Hsu.

4 recordsLinked to original sources
PubMed1979

Accelerated mineralization of two organophosphate insecticides in the rhizosphere.

Numerous xenobiotic compounds, including the organophosphate insecticides O, O-diethyl-O-(2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate (diazinon) and O, O-diethyl-O-p-nitrophenyl phosphorothioate (parathion), appear to be degraded in the soil environment by an initial cometabolic attack. Comparing the mineralization rates of radiolabeled diazinon and parathion in root-free and in rhizosphere soil, we tested our hypothesis that, because of the presence of root exudates, the rhizosphere is an especially favorable environment for such co-metabolic transformations. The insecticides were added individually at 5 mug/g to sealed flasks containing either soil permeated by the root system of a bush bean plant or identical soil without roots. Periodically, the flask atmospheres were flushed through traps and the evolved (14)CO(2) was quantitated. Bush bean plant roots without associated rhizosphere microorganisms failed to produce a significant amount of (14)CO(2). During 1 month of incubation, rhizosphere flasks mineralized 12.9 and 17.9% of the added diazinon and parathion radiocarbon, respectively, compared to 5.0 and 7.8% by the soil without roots. The mineralization of parathion but not of diazinon was stimulated in a similar manner when soil without roots was repeatedly irrigated with a root exudate produced in aseptic solution culture. Viable counts of microorganisms on soil extract agar were not significantly altered by root permeation or by root exudate treatment of the soil, leaving population selection and/or enhanced cometabolic activity as the most plausible interpretations for the observed stimulatory effects. Rhizosphere interactions may substantially shorten the predicted half-lives of some xenobiotic compounds in soil.

Bacteria↗
PubMed1975

Molecular conformation of bovine A1 basic protein, a coiling macromolecule in aqueous solution.

Aqueous solutions of bovine A1 protein, the major component of the basic protein fraction of myelin, were studied by small angle X-ray diffraction. The experimentally determined molecular weight, 17,800, is within 3% of that corresponding to the amino acid sequence, 18, 395, and the radius of gyration was found to be 46.3 A. No equivalent scattering particle of uniform electron density could be found which was compatible with all parameters evaluated from the diffraction measurements. The possibility of a coiled shape was therefore investigated using a worm-like chain model. This yielded a contour length of 439 A and a persistence length of 15.7 A. The radius of gyration of this model chain, 47.1 A, is in quite reasonable accord with the experimental value. The latter, after correction for excluded volume effects and finite chain length, yields for the characteristic ratio, ro2/nplp-2, 5.4. This may be compared with the value, 6.1, obtained after applying a correction for finite chain length to the viscosity data given by Tanford et al. for 12 proteins in 6 M guanidine hydrochloride and 0.1 M beta-mercaptoethanol. These two experimental values fall in the expected order, since the 15% glycine content of the A1 protein is considerably higher than the average for other proteins, which is about 8%. The corresponding values predicted from conformational calculations by Miller et al. for random copolymers of the L-alanine-glycine type are 5.9 (18% glycine) and 7.0 (8% glycine). We conclude that the A1 protein exists predominately, if not exclusively, as a random coil in aqueous solution.

Animals↗