Biomedical subjects

D Q Zhao

Publications and source records attributed to D Q Zhao.

5 recordsLinked to original sources

PubMed2005

Amorphous metallic plastic.

We report cerium-based bulk metallic glasses with an exceptionally low glass transition temperature Tg, similar to or lower than that of many polymers. We demonstrate that, in near-boiling water, these materials can be repeatedly shaped, and can thus be regarded as metallic plastics. Their resistance to crystallization permits extended forming times above Tg and ensures an adequate lifetime at room temperature. Such materials, combining polymerlike thermoplastic behavior with the distinctive properties of metallic glasses, are highly unusual for metallic alloys and have great potential in applications and can also facilitate studies of the supercooled liquid state.

Journal Article↗

PubMed2005

Fracture of brittle metallic glasses: brittleness or plasticity.

We report a brittle Mg-based bulk metallic glass which approaches the ideal brittle behavior. However, a dimple structure is observed at the fracture surface by high resolution scanning electron microscopy, indicating some type of "ductile" fracture mechanism in this very brittle glass. We also show, from the available data, a clear correlation between the fracture toughness and plastic process zone size for various glasses. The results indicate that the fracture in brittle metallic glassy materials might also proceed through the local softening mechanism but at different length scales.

Journal Article↗

PubMed2001

Human catalytic antibodies with glutathione peroxidase activity.

In order to generate catalytic antibodies with glutathione peroxidase (GPx) activity, we prepared GSH-S-DNP butyl ester and GSH-S-DNP benzyl ester as the haptens. Two ScFvs that bound specifically to the haptens were selected from the human phage-displayed antibody library. The two ScFv genes were highly homologous, consisting of 786 bps and belonging to the same VH family-DP25. In the premise of maintaining the amino acid sequence, mutated plasmids were constructed by use of the mutated primers in PCR, and they were over-expressed in E. coli. After the active site serine was converted into selenocysteine with the chemical modifying method, we obtained two human catalytic antibodies with GPx activity of 72.2U/micromol and 28.8U/micromol, respectively. With the aid of computer mimicking, it can be assumed that the antibodies can form dimers and the mutated selenocysteine residue is located in the binding site. Furthermore, the same Ping-Pong mechanism as the natural GPx was observed when the kinetic behavior of the antibody with the higher activity was studied.

Amino Acid Sequence↗

PubMed2001

[An abzyme to catalytize the deiodination of thyroxine].

AIM: To mimic an important family of selenoenzymes in organism-thyroxine (T4) deiodinases and prepare a selenium-containing abzyme catalyzing deiodination of T4. METHODS: A anti-T4 monoclonal antibody was generated by hybridoma methodology and converted into a selenium-containing abzyme by the method of chemical modification. The catalytic activity of the enzyme was measured by RIA method. RESULTS: The abzyme displayed a marked activity of catalyzing deiodination of T4 and a higher specificity to the substrate T4 than that of natural enzyme, and the double reciprocal plots of the initial rates of T3 formation vs. T4 concentration yielded a family of parallel lines. The catalytic activity could be sensitively inhibited by 6-propyl-2-thiouracil (PTU), a competitive inhibitor for dithiothreitol (DTT). CONCLUSION: An abzyme with the diodination activity was first prepared and the reaction mechanism of the enzyme was bisubstrate ping-pong one.

Animals↗

PubMed1999

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of phospholipase A2 and fibrinolytic enzyme, two enzymes obtained from Chinese Agkistrodon blomhoffii Ussurensis venom.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to analyze two enzymes, phospholipase A2 and fibrinolytic enzyme isolated from Chinese Agkistrodon blomhoffii Ussurensis venom. Using sinapinic acid as the matrix, positive ion mass spectra of the enzymes were obtained. In addition to the dominant protein [M + H]+ ions, multimeric and multiply charged ions were also observed in the mass spectra. The higher the concentration of the enzymes, the more multiply charged polymer and multimeric ions were detected. Our results indicate that MALDI-TOFMS can provide a rapid and accurate method for molecular weight determination of snake venom enzymes. Mass accuracies of 0.1 and 0.3% were achieved by analysis of highly dialyzed phospholipase A2 and fibrinolytic enzyme, and these results are much better than those obtained using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. MALDI-TOFMS thus provides a reliable method to determine the purity and molecular weight of these enzymes, which are of potential use as therapeutants.

Agkistrodon↗