Abstract
Glutathione transferase zeta (GSTZ1-1) catalyzes the cis-trans isomerization of maleylacetoacetate and the biotransformation of a range of α-haloacids. The objective of this study was to determine the kinetics of the biotransformation of maleylacetone (MA), an analogue of the natural substrate maleylacetoacetate, and chlorofluoroacetic acid (CFA) by polymorphic variants of recombinant hGSTZ1-1. The kcat of the four variants of hGSTZ1-1 with MA as the substrate followed the order: 1c-1c > 1b-1b > 1d-1d > 1a-1a whereas the kcat for the biotransformation of CFA followed the order: 1a-1a > 1b-1b ∼ 1c-1c ∼ 1d-1d. The turnover rates of MA were much higher than those of CFA for each variant and ranged from 22-fold (1a-1a) to 980-fold differences (1c-1c). The catalytic efficiencies of hGSTZ1-1 variants with MA as the substrate were much greater than those with CFA as the substrate, but little difference among the polymorphic variants was observed. MA was a mixed inhibitor of all variants with CFA as substrate: the mean competitive inhibition constant (KicMA) for all variants was about 100 μM and the mean uncompetitiv- inhibition constant (KiuMA) was about 201 μM. Hence, MA and α-haloacids apparently compete for the same active site on the enzyme. DCA-induced inactivation of the four variants showed that the inactivated enzymes show markedly reduced isomerase activities. The residual activities were different for each variant: 1a-1a (12%) > 1b-1b ∼ 1c-1c ∼ 1d-1d (<5%). This is the first kinetic analysis of polymorphic variants of hGSTZ1-1, and the similarity of the kinetic constants for hGSTZ1-1 variants with either MA or CFA as substrates indicates that few differences in DCA-induced perturbations of tyrosine metabolism would likely be observed in humans.
Original language | English |
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Pages (from-to) | 957-963 |
Number of pages | 7 |
Journal | Chemical Research in Toxicology |
Volume | 15 |
Issue number | 7 |
DOIs | |
Publication status | Published - 2002 |