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T Shen

Publications and source records attributed to T Shen.

101 records · Page 6Linked to original sources
PubMed1983

Restriction endonuclease cleavage map of mitochondrial DNA from Peking duck liver.

Mitochondrial DNA of the liver from Peking duck was cleaved by restriction endonucleases EcoRI, BamHI, PstI and BglI into 1, 2, 4 and 5 fragments, respectively, while the BglII was without any cleavage. The restriction map of this mtDNA was constructed by measuring the length of restriction fragments using both electrophoresis analysis and electron microscopy. The position of D-loop and the direction of replication of the mtDNA were also determined.

Animals↗
PubMed1982

RNA recombination: --introducing poly(A) into Q beta phage.

Poly(A) molecule is inserted between two Q beta RNA molecules which have been partially degraded, one from the 3'-end and another from the 5'-end. E. coli HfrH is infected with these mosaic RNA molecules and a few recombined phages carrying poly(A) are obtained. Analysis of the RNA of 907 phage (one of these recombination phages) shows that the chain length of the poly(A) it contained is about 40.

Coliphages↗
PubMedDate not supplied

An improved method for isolation and identification of Zn-metallothionein from cadmium-induced rat liver.

Zn-metallothioneins (MT-1 and MT-2) were isolated and purified from Wistar rat liver induced by subcutaneous injection with cadmium chloride over a short time. Instead of Sephadex G-50 and DEAE Sephadex A-50, new chromatographic media produced by Pharmacia, Sephacryl S-200, S-100 and DEAE Sepharose Fast Flow were used in the purification of metallothioneins. The time required for purification with the new method was only 1/3 that required with the usual method and had the same purification effect and rate of recovery. The number of mercapto groups measured with modified Ellman's reagent and cysteine as standard is 20 in MT molecules. Zn and Cd concentrations in each fraction were measured by single sweep polarography rather than atomic absorption spectrophotometry. MT-1 and MT-2 contained 6 gram atoms of zinc, but no cadmium. Purified MT-1 and MT-2 were shown by high performance liquid chromatographic analysis to be highly homogeneous and had an amino acid composition similar to that of Cd-MT.

Amino Acids↗
PubMedDate not supplied

The mechanism of stimulation of NADPH oxidation during the mechanism-based inactivation of cytochrome P450 2B1 by N-methylcarbazole: redox cycling and DNA scission.

The oxidation rate of NADPH is markedly stimulated during the mechanism-based inactivation of cytochrome P450 2B1 by N-methylcarbazole (NMC) in a reconstituted system consisting of NADPH-cytochrome P450 reductase, cytochrome P450 and phospholipid. The stimulation of NADPH oxidation in this system is due to 1-hydroxy-N-methylcarbazole (1-OH-NMC), one of the major metabolites of NMC. The 1-OH-NMC is further metabolized in an NADPH-dependent manner by the reconstituted system or by purified NADPH-cytochrome P450 reductase to give a more polar metabolite which has been isolated by HPLC. The conversion of 1-OH-NMC to this product was inhibited by superoxide dismutase (SOD), and incubation of the 1-OH-NMC with hypoxanthine-xanthine oxidase resulted in the formation of the same product, suggesting that the superoxide anion was involved in the metabolism of 1-OH-NMC by the reductase. Redox cycling activity during the metabolism of 1-OH-NMC by reductase has been demonstrated. The oxidation of NADPH by the reductase in the presence of 35 microM 1-OH-NMC was enhanced approximately 23-fold [240 nmol of NADPH oxidized/(min.nmol of reductase)] relative to control levels in the presence of 500 microM NMC [10.5 nmol/(min.nmol of reductase)]. 1-OH-NMC (35 microM) caused a 40-fold increase in the rate of formation of superoxide during its metabolism by reductase. The rapid rates of NADPH oxidation and superoxide formation were inhibited by the addition of reduced glutathione (GSH) to the reaction mixture. Neither SOD nor GSH inhibited the reductase activity directly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Multidrug resistance-associated protein (MRP) mediated transport of daunomycin and leukotriene C4 (LTC4) in isolated plasma membrane vesicles.

Studies have been carried out to examine in vitro drug transport in plasma membrane vesicles isolated from HL60/ADR cells that overexpress MRP. The results demonstrate that glutathione (GSH) enhances transport of daunomycin. A greater increase in transport activity occurs when the reaction is carried out in the presence of both GSH and sodium chloride. Sodium chloride alone has no effect on daunomycin transport. It has also been observed that GSH in the presence of sodium chloride induces a major increase in the transport level of LTC4. Thus far, no metal ion other than sodium chloride has been found to be active in the drug transport system. Kinetic analysis reveals that GSH in the presence of sodium chloride greatly reduces Km and increases Vmax, for daunomycin. Additional studies show that ATPase activity in isolated plasma membrane from HL60/ADR cells is greatly enhanced in the presence of both GSH and sodium chloride. These results suggest the possibility that GSH and sodium chloride stimulate MRP-mediated transport as a result of increased ATPase activity.

ATP-Binding Cassette Transporters↗
PubMedDate not supplied

Inactivation of purified rat liver cytochrome P-450 2B1 and rabbit liver cytochrome P-450 2B4 by N-methylcarbazole.

Metabolism of N-methylcarbazole by purified rat liver cytochrome P-450 2B1 or rabbit liver P-450 2B4 resulted in the inactivation of these enzymes in a time-dependent, pseudo-first order manner as assayed spectrally by the decrease in the reduced CO spectrum at 450 nm. The inactivation was saturable with respect to the concentration of N-methylcarbazole, and a Ki = 5.2 microM and kINACT = 0.14 min-1 were determined for the inactivation of P-450 2B1. For P-450 2B4 inactivation, the Ki was 23 microM and the kINACT = 0.21 min-1. There was no increase in the reduced CO spectrum at 420 nm accompanying the inactivation, and the slight loss of the P-450 heme prosthetic group, as determined by the spectrum at 418 nm, was not sufficient to account for the loss of the reduced CO spectrum at 450 nm. The metabolism of N-methylcarbazole by P-450 did not result in the formation of a metabolic intermediate complex, which could also be responsible for the loss of cytochrome P-450 activity. Loss of catalytic activity for further substrate metabolism was also observed after preincubation of enzyme with N-methylcarbazole and the loss of catalytic activity correlated with the loss of the reduced CO spectrum. Accompanying the loss of spectrally detectable P-450 2B1 and P-450 2B4 catalytic activity, there was an increase in the NADPH oxidation rate. This increased rate persisted on subsequent addition of NADPH.

Animals↗