| Co-Investigator(Kenkyū-buntansha) |
HATAYAMA Ichiro Hirosaki University School of Medicine, Second Depatment of Biochemistry, Assist, 医学部, 講師 (40133871)
SATOH Kimihiok Hirosaki University School of Medicine, Second Depatment of Biochemistry, Associ, 医学部, 助教授 (70003655)
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| Research Abstract |
(1) The activities of human glutathione S-transferase-pi (GST-pi) and GST-mu were dose-dependently inhibited by hematoporphyrin, an activator of guanylate cyclase. The concentrations of humatoporphyrin to give a 50% inhibition of activity (IC_<50>) were 14,2 muM for GST-pi and 2.2 muM for GST-mu. Nitroprusside, a compound to release nitric oxide (NO), inhibited the activities of GST-pi, GST-mu, and GST-alpha, IC_<50> values of nitroprusside being 0.04 - 0.14 muM.Nitrite (NO_2) did not inhibit the activities of GST-pi or GST-alpha, but inhibited GST-mu activity, with an IC_<50> value of 0.39 muM.Since the Km values for nitroglycerin are 1.1-2.5 muM in Mu class GST forms, nitrite released from nitroglycerin by these enzymes is suggested to inhibit their activities.
(2) Recombinant rat GST-P expressed in Escherichia coli was shown to bind heme. Furthermore, E.coli expressing GST-P were more sensitive to hydrogen peroxide treatment and exibited reduced expression of catalase and several oth
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er proteins than E.coli not expressing GST-P.
(3) Experiments utilizing GST-P mutants whose cysteine residues were independently substituted with alanine by site-directed mutagenesis revealed that inactivation by hydrogen peroxide was mainly due to disulfide bond formation between the 47th and 101st cysteine residues. Since all mutants have similar specific activities to that of the wild type, none of the four cysteine residues is essential for GST-P activity but the 47th and 101st cysteine residues may be located in an important region for glutathione binding, disulfide bond formation between these residues resulting in steric hindrance. These mutants also revealed that inactivation by N-ethylmaleimide was due to the binding of the SH-reagent to the 47th cysteine residue.
(4) The effects of peroxisome proliferator administration and x-ray irradiation on expression of Pi class GST forms were investigated. Both treatments, known to induce the procuction of active oxygen species, resulted in the repressed expression of these forms. Less
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