Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.10.3.3 (ascorbate oxidase)
 778 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chromium(VI) reductase activity was measured in ultrafiltrates of rat lung after various pretreatments in vitro at 37 degrees C and pH 7.0. Pretreatment of ultrafiltrates with L-ascorbate oxidase (EC 1.10.3.3), which specifically eliminated ascorbate, blocked approximately 95% of chromium(VI) reductase activity in ultrafiltrates. Preincubation of ultrafiltrates with heat-denatured ascorbate oxidase or the sulfhydryl-blocking agent N-ethylmaleimide (NEM) had no significant effect on Cr(VI) reductase activity. In rat lung cytosols, L-ascorbate oxidase blocked approximately 95% and NEM blocked approximately 15% of Cr(VI) reductase activity. The extent of inhibition of Cr(VI) reductase activity in cytosols by L-ascorbate oxidase was significantly decreased to approximately 75% after addition of 1.0 mM NADPH. When Cr(VI) was incubated with salmon sperm nuclei suspended in rat lung cytosol for 15 min, Cr became bound to nuclear DNA. This Cr-DNA binding was completely inhibited by preincubation of rat lung cytosols with L-ascorbate oxidase and inhibited approximately 60% by preincubation with NEM. Taken together these data suggest that ascorbate and/or ascorbate-dependent factors are the principal reductants of Cr(VI) in both ultrafiltrates and cytosols prepared from rat lung and ascorbate-dependent metabolism of Cr(VI) results in Cr binding to nuclear DNA in vitro. Although sulfhydryl-containing factors and NADPH-dependent factors only make a minor contribution to Cr(VI) reduction in rat lung cytosols, sulfhydryls may be significantly involved in the binding of Cr to nuclear DNA.
Carcinogenesis 1992 Aug
PMID:Ascorbate is the principal reductant of chromium(VI) in rat lung ultrafiltrates and cytosols, and mediates chromium-DNA binding in vitro. 149 83

Chromium (VI) reductase activity was measured in ultrafiltrates of rat liver and kidney after various pretreatments in vitro at 37 degrees C and pH 7.0. Preincubation of ultrafiltrates with L-ascorbate oxidase (EC 1.10.3.3), which specifically eliminated ascorbate, blocked approximately 80% of the Cr(VI) reductase activity. Heat-denatured ascorbate oxidase had no effect on Cr(VI) reductase activity in ultrafiltrates. Preincubation of ultrafiltrates with N-ethylmaleimide, which non-specifically blocked sulfhydryls, including reduced glutathione, decreased Cr(VI) reductase activity by only 20%. Treatment of male Sprague-Dawley rats with phorone decreased non-protein sulfhydryl (NPSH) levels in rat liver by greater than 90% and tripled reduced ascorbate levels 2 h after treatment. Ultrafiltrates of liver prepared from phorone-treated rats had twice the Cr(VI) reductase activity of control ultrafiltrates, and greater than 95% of this activity could be blocked by preincubation with ascorbate oxidase. Treatment of rats with sodium dichromate (20 mg/kg) caused a significant decrease in ascorbate levels in kidney but not liver, and no change in NPSH levels in kidney or liver, 15 min after treatment. We conclude that ascorbate is the major reductant of Cr(VI) in rat liver and kidney ultrafiltrates and may well be the major non-enzymatic reductant of Cr(VI) in rat liver and kidney in vivo.
Carcinogenesis 1991 Sep
PMID:Ascorbate is the principal reductant of chromium (VI) in rat liver and kidney ultrafiltrates. 189 33