Structure-activity relationships for the glutathione conjugation of 2-substituted 1-chloro-4-nitrobenzenes by rat glutathione S-transferase 4-4.
In the present study structure--activity relationships (SAR's) are described for the experimentally determined kinetic parameters (Km, kappa cat, and kappa cat/Km) of the GST 4-4-catalyzed reaction between GSH and 10 2-substituted 1-chloro-4-nitrobenzenes. Steric, lipophilic, and electronic parameters were correlated with the kinetic parameters. Moreover, charge distributions and several energy values were calculated for the substrates and the corresponding Meisenheimer intermediates with MeS- as a model nucleophile for the thiolate anion of GSH and used in the regression analyses. The correlations obtained were compared with the corresponding SAR's for the base-catalyzed GSH conjugation reaction at pH 9.2. A high correlation coefficient was found between the kinetic parameter kappa s for the base-catalyzed reaction and the Hammett substituent constant (sigma p). Much lower correlation coefficients were obtained with kappa cat and sigma p and with kappa cat/Km and sigma p. Moreover, the reaction constant rho was significantly higher for the base-catalyzed than for the enzyme-catalyzed reaction. Also, high correlations were found between the kinetic parameters and the charges on the p-nitro substituent in the substrates. When kappa s was plotted against these charges, a linear relationship was found in which the slope was larger than the slope of a corresponding plot with kappa cat/Km. The Hammett sigma p can be divided into an inductive (F) and a resonance (R) component. With multiple regression between the kinetic parameters and F and R, higher correlation coefficients were obtained than with sigma p alone. Our observations suggest that the transition states for the base-catalyzed and the GST 4-4-catalyzed GSH conjugation reaction are different. Moreover, single classical physiochemical and computer-calculated molecular parameters and combinations of them can be an alternative approach for examining SAR's for spontaneous and GST-catalyzed GSH conjugation reactions.
van der Aar
E M
EM
Department of Pharmacochemistry, Vrije Universiteit, Amsterdam, Netherlands.
de Groot
M J
MJ
Bijloo
G J
GJ
van der Goot
H
H
Vermeulen
N P
NP
D000818:Animals; D005978:Glutathione / Q000737:chemistry* / Q000378:metabolism*; D005982:Glutathione Transferase / Q000737:chemistry* / Q000378:metabolism*; D009578:Nitrobenzenes / Q000737:chemistry* / Q000493:pharmacokinetics*; D011485:Protein Binding; D051381:Rats; D012984:Software; D013329:Structure-Activity Relationship
D009578:Nitrobenzenes; C010407:4-chloronitrobenzene; D005982:Glutathione Transferase; D005978:Glutathione