Biomedical subjects

Yu Xue

Publications and source records attributed to Yu Xue.

22 records · Page 2Linked to original sources

PubMed2003

Continuum traffic model with the consideration of two delay time scales.

This paper presents a continuum traffic model. The derivation of this model is based upon the assumption that the stream velocity u reaches the equilibrium velocity u(e) within the relaxation time T, while the equilibrium velocity u(e) is adjusted to be attained through the driver's reaction time t(r). It is also assumed that the former delay time scale is greater than the latter. A motion equation with nonconstant propagation velocity of a disturbance in traffic flow is derived that can reflect the anisotropy of disturbance propagation in real traffic, unlike some other higher-order continuum models. It indicates that in our model the undesirable "wrong-way travel" phenomenon and gas-like behavior have been eliminated. The formation and diffusion of traffic shock can be better simulated.

Journal Article↗

PubMed2003

Structural basis of heroin and cocaine metabolism by a promiscuous human drug-processing enzyme.

We present the first crystal structures of a human protein bound to analogs of cocaine and heroin. Human carboxylesterase 1 (hCE1) is a broad-spectrum bioscavenger that catalyzes the hydrolysis of heroin and cocaine, and the detoxification of organophosphate chemical weapons, such as sarin, soman and tabun. Crystal structures of the hCE1 glycoprotein in complex with the cocaine analog homatropine and the heroin analog naloxone provide explicit details about narcotic metabolism in humans. The hCE1 active site contains both specific and promiscuous compartments, which enable the enzyme to act on structurally distinct chemicals. A selective surface ligand-binding site regulates the trimer-hexamer equilibrium of hCE1 and allows each hCE1 monomer to bind two narcotic molecules simultaneously. The bioscavenger properties of hCE1 can likely be used to treat both narcotic overdose and chemical weapon exposure.

Binding Sites↗

PubMed2003

[Nitrogen removal in a pilot-scale zeolite reed bed system].

In this study, the nitrogen removal efficacy of a pilot-scale zeolite reed bed system was tested for the treatment of agricultural wastewater and domestic wastewater etc. At a mean hydraulic loading of 0.6 m/d, the total nitrogen, ammonia, nitrate, nitrite in winter and spring were reduced across the system by 38.9% and 58.2%, 93.11% and 78.84%, 10.01% and 48.99%, 38.81% and 98.45%, respectively. The system performance in spring was much better than in winter. Under the same conditions, the total nitrogen, ammonia, nitrate removal rate of zeolite reed bed were 28%, 67%, 35% higher than that of gravel reed bed. The ammonia adsorption and ion exchange on zeolite and biological nitrogen removal through nitrification and denitrification were the main removal mechanism of nitrogen in the zeolite reed bed.

Adsorption↗

PubMed2002

A minimal exonuclease domain of WRN forms a hexamer on DNA and possesses both 3'- 5' exonuclease and 5'-protruding strand endonuclease activities.

Werner syndrome is a rare autosomal recessive disease characterized by a premature aging phenotype, genomic instability, and a dramatically increased incidence of cancer and heart disease. Mutations in a single gene encoding a 1432-amino acid helicase/exonuclease (hWRN) have been shown to be responsible for the development of this disease. We have cloned, overexpressed, and purified a minimal, 171-amino acid fragment of hWRN that functions as an exonuclease. This fragment, encompassing residues 70-240 of hWRN (hWRN-N(70-240)), exhibits the same level of 3'-5' exonuclease activity as the previously described exonuclease fragment encompassing residues 1-333 of the full-length protein. The fragment also contains a 5'-protruding DNA strand endonuclease activity at a single-strand-double-strand DNA junction and within single-stranded DNA, as well as a 3'-5' exonuclease activity on single-stranded DNA. We find hWRN-N(70-240) is in a trimer-hexamer equilibrium in the absence of DNA when examined by gel filtration chromatography and atomic force microscopy. Upon addition of DNA substrate, hWRN-N(70-240) forms a hexamer and interacts with the recessed 3'-end of the DNA. Moreover, we find that the interaction of hWRN-N(70-240) with the replication protein PCNA also causes this minimal, 171-amino acid exonuclease region to form a hexamer. Thus, the active form of this minimal exonuclease fragment of human WRN appears to be a hexamer. The implications these results have on our understanding of hWRN's roles in DNA replication and repair are discussed.

Amino Acid Sequence↗