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S-Acyl Glutathione Thioesterase of Plant Tissue ¹

^a Department of Biochemistry and Statewide Air Pollution Research Center, University of California, Riverside, California 92502

The enzymic hydrolysis of S-acyl glutathione has been observed in extracts of various plant tissues. The richest source found in this study was avocado mesocarp. No enzymic activity was observed with acetyl coenzyme A or acetylthiocholine as substrates. Hydrolytic activity was essentially constant in the pH range 7 to 9. There was a break in the activation energy plot at 25 C with activation energy above that point being 6800 calories and 2600 calories below it. The Michaelis constants for S-acetyl, S-propionyl, and S-butyryl glutathione were 200, 80, and 15 µM, respectively. The data are not consistent with the hypothesis that variation in the phytotoxicity of peroxyacyl nitrates is a function of the ability of the plant to hydrolyze glutathione thioesters.