Glutathione S-transferase activities of S-Type and L-type thioltransferases from Arabidopsis thaliana

Abstract

The glutathione S-transferase (GST) activities of S-type and L-type thioltransferases (TTases), which are purified from the seeds and leaves of Arabidopsis thaliana, respectively, were identified and compared. The S-type and L-type TTases showed K-m, values of 9.72 mM and 3.18 mM on 1-chloro-2,4-dinitrobenzene (CDNB), respectively, indicating the L-type TTase has higher affinity for CDNB. The GST activity of the L-type TTase was rapidly inactivated after being heated at 70 degrees C or higher. The GST activity of the S-type TTase remains active in a range of 30-90 degrees C. Hg2+ inhibited the GST activity of the S-type TTase, whereas Ca2+ and Cd2+ inhibited the GST activity of the L-type TTase. Our results suggest that the GST activities of two TTases of Arabidopsis thaliana may have different catalytic mechanisms. The importance of the co-existence of TTase and GST activities in one protein remains to be elucidated.