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Biomedical subjects

S M Liu

Publications and source records attributed to S M Liu.

At least 109 records · Page 6Linked to original sources
PubMed1985

Formate dehydrogenase molybdenum and tungsten sites--observation by EXAFS of structural differences.

Preliminary EXAFS data has been collected on the molybdenum (K-edge) in C. pasteurianum formate dehydrogenase and the tungsten (LIII-edge) in C. thermoaceticum formate dehydrogenase. In the presence of dithionite, the tungsten enzyme was devoid of W = O bonds, and exhibited average W-(O, N) and W-S bond lengths of 2.13 +/- 0.03 A and 2.39 +/- 0.03 A, respectively. In sharp contrast, the C. pasteurianum molybdenum site has three Mo = O bonds with an average bond length of 1.74 +/- 0.03 A. It is also the first molybdenum enzyme found lacking Mo-S bonds, and does not appear to be redox active in the presence of formate or dithionite. Model compounds WO2(8-hydroxyquinoline)2 = WO2(ox)2, and WO2(8 mercaptoquinoline)2 = WO2(tox)2, were also examined. Respective predicted bond lengths for WO2(ox)2 and WO2(tox)2 were W = O of 1.71, 1.73 A; W-N of 2.31, 2.29 A; W-O or W-S of 1.92 or 2.40 A, with estimated uncertainties of +/- 0.03 A.

Aldehyde Oxidoreductases↗
PubMed1985

Effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine on the growth and viral capsid antigen expression of Epstein-Barr virus-associated tumor (B-95-8) cells transplanted to nude mice.

When persistently Epstein-Barr virus (EBV)-infected lymphoblastoid (B-95-8) cells were transplanted subcutaneously or intracerebrally to nude mice of either BALB/c or NIH background, tumors developed, and the tumor cells spontaneously expressed viral capsid antigen (VCA). This model was used to evaluate the in vivo anti-EBV activity of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU), a highly potent and selective antiherpes agent, which was recently shown to inhibit several parameters of EBV infection in vitro. When administered intraperitoneally at 200 mg/kg/day for 4 weeks, or 500 mg/kg/day for 2 weeks, starting immediately after B-95-8 cell inoculation, BVDU effectively reduced tumor growth and VCA expression of either subcutaneously or intracerebrally inoculated B-95-8 cells.

Animals↗
PubMed1983

Purification and properties of NADP-dependent formate dehydrogenase from Clostridium thermoaceticum, a tungsten-selenium-iron protein.

NADP-dependent formate dehydrogenase (NADP+) (EC 1.2.1.43) from Clostridium thermoaceticum has been purified to a specific activity of about 1100 mumol min-1 mg-1 when assayed at 55 degrees C and pH 7.5. The enzyme is extremely oxygen-sensitive and 7.6 microM of O2 causes 50% inhibition of initial velocity under assay conditions. Purification was done in an atmosphere at 95% N2 and 5% H2 and by including azide, dithionite, and glycerol as stabilizing agents in all buffer solutions. The enzyme contains, in molar ratios, 2 tungsten, 2 selenium, 36 iron, and about 50 inorganic sulfur. It has a molecular weight of about 340,000 and consist of two each of two different subunits giving the composition alpha 2 beta 2. The molecular weight of the alpha-subunit is 96,000 and that of the beta-subunit is 76,000. The selenium resides in the two alpha-subunits. Tungsten is released from the protein on denaturation and may exist as a tungsten cofactor. The enzyme catalyzes a reduction of CO2 with NADPH at pH 7.5 and 55 degrees C and Keq at these conditions is (2.35 +/- 0.49) x 10(-2) if CO2 is considered the active species and (1.48 +/- 0.31) x 10(-3) if HCO3- is the active species.

Aerobiosis↗