| Autor: |
Allardyce CS; Centre for Mechanisms of Human Toxicity, University of Leicester, PO Box 138, Lancaster Road, Leicester LE1 9HN, UK., McDonagh PD, Lian LY, Wolf CR, Roberts GC |
| Jazyk: |
angličtina |
| Zdroj: |
The Biochemical journal [Biochem J] 1999 Nov 01; Vol. 343 Pt 3, pp. 525-31. |
| Abstrakt: |
Glutathione S-transferases (GSTs) play a key role in the metabolism of drugs and xenobiotics. To investigate the catalytic mechanism, substrate binding and catalysis by the wild-type and two mutants of GST A1-1 have been studied. Substitution of the 'essential' Tyr(9) by phenylalanine leads to a marked decrease in the k(cat) for 1-chloro-2,4-dinitrobenzene (CDNB), but has no affect on k(cat) for ethacrynic acid. Similarly, removal of the C-terminal helix by truncation of the enzyme at residue 209 leads to a decrease in k(cat) for CDNB, but an increase in k(cat) for ethacrynic acid. The binding of a GSH analogue increases the affinity of the wild-type enzyme for CDNB, and increases the rate of the enzyme-catalysed conjugation of this substrate with the small thiols 2-mercaptoethanol and dithiothreitol. This suggests that GSH binding produces a conformational change which is transmitted to the binding site for the hydrophobic substrate, where it alters both the affinity for the substrate and the catalytic-centre activity ('turnover number') for conjugation, perhaps by increasing the proportion of the substrate bound productively. Neither of these two effects of GSH analogues are seen in the C-terminally truncated enzyme, indicating a role for the C-terminal helix in the GSH-induced conformational change. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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