Computational modeling of the microsomal glutathione transferase-I-catalyzed reaction of glutathione with halogenated alkenes

Halogenated alkenes are widely used in industrial and commercial applications and some are carcinogenic in rodents. The mechanism of bioactivation of halogenated alkenes includes hepatic glutathione conjugation catalyzed by cytosolic and microsomal glutathione transferases, enzymatic hydrolysis by γ-glutamyltransferase and aminopeptidase M or cysteinylglycine dipeptidase to yield the corresponding cysteine conjugates, and finally, bioactivation of the cysteine conjugates to reactive species by cysteine conjugate β-lyase.; The products that result from the reaction of glutathione with halogenated alkenes may be addition products, substitution products, or both. The different glutathione conjugates of a halogenated alkene are metabolized and excreted at different rates, follow different metabolic pathways, and exhibit different toxicity. Microsomal glutathione transferase-I-catalyzed conjugation of chlorotrifluoroethene is regioselective and stereoselective, whereas the cytosolic glutathione transferase-catalyzed reaction is regioselective but not stereoselective. The ratio of addition product to substitution product resulting from the reaction of glutathione with hexafluoropropene and 2-(fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A) differs depending on whether the reaction is catalyzed with rat liver cytosolic proteins or rat liver microsomal proteins. These data suggest that the ratio of glutathione conjugates may differ depending on whether the reaction is catalyzed by cytosolic glutathione transferases or microsomal glutathione transferase-I (mGST-I).; The aim of this thesis research was to develop computational approaches to predict the outcome of the microsomal glutathione transferase-I-catalyzed reaction of glutathione with halogenated alkenes. A quantitative structure-activity relationship was developed that relates the specific activity of the microsomal glutathione transferase-I-catalyzed reaction with the lowest unoccupied molecular orbital (LUMO) energy of halogenated alkenes. The results indicated that mGST-I was competent to catalyze the glutathione conjugation of halogenated alkenes with LUMO energies less than −0.589 eV.; An ab initio computational study of the reaction of ethanethiolate, a surrogate for glutathione, with the chlorotrifluoroethene, hexafluoropropene, and compound A was conducted. An empirical study was conducted to quantify the distribution of addition and substitution products that resulted from the mGST-I-catalyzed reaction of glutathione with these halogenated alkenes. The results indicated that this computational approach accurately predicted the distribution of the addition and substitution products resulting from the mGST-I-catalyzed reaction of glutathione with these halogenated alkenes.