ADP-ribose pyrophosphatase-I partially purified from livers of rats overdosed with acetaminophen reveals enzyme inhibition in vivo reverted in vitro by dithiothreitol
✍ Scribed by João Meireles Ribeiro; María Jesús Costas; José Carlos Cameselle
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 104 KB
- Volume
- 13
- Category
- Article
- ISSN
- 1095-6670
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✦ Synopsis
Free ADP-ribose reacts nonenzymatically with proteins and can lead to intracellular damage. The low-K m ADP-ribose pyrophosphatase-I (ADPRibase-I) is well suited to control free ADP-ribose and nonenzymatic ADP-ribosylation. In vitro, the acetaminophen metabolite N-acetyl-p-benzoquinoneimine (NAPQI) decreases ADPRibase-I V max and increases K m , effects not reverted by dithiothreitol (DTT) and attributed to enzyme arylation. The present study was conducted to test whether acetaminophen overdose affected AD-PRibase-I in vivo. Rats pretreated with 3-methylcholanthrene and L-buthionine-[S,R]-sulfoximine to potentiate acetaminophen toxicity received an intraperitoneal dose of either acetaminophen (800 mg/ kg; n 5) or vehicle (n 3). ADPRibase-I partially purified from acetaminophen-overdosed rats showed a decreased V max (0.32 ؓ 0.09 versus 0.60 ؓ 0.03 mU/mg of liver protein; p Ͻ 0.01) not reverted by DTT and an increased K m for ADP-ribose (1.39 ؓ 0.31 versus 0.67 ؓ 0.05 lM; p Ͻ 0.01) that, contrary to the in vitro NA-PQI effect, was reverted by DTT. Incubation of partially purified ADPRibase-I from normal rat liver with oxidized glutathione elicited a time-and dose-dependent, DTT-reverted increase of K m , without change of V max . The results indicate that the activity of ADPRibase-I can be regulated by thiol exchange and that the increase of K m elicited by acetaminophen overdosage was related to the oxidative stress caused by the drug. It remains to be seen whether an increase of free ADPribose concomitant to ADPRibase-I inhibition could contribute to the hepatotoxicity of acetaminophen.