50
Richard H. Shimabukuro et al.
~H2
~H-COCH2CH2CHCOOH
9HCONHCH2COOH
9 H2
+ GSH ....:G:..::S~H....:-A,.:..:r.!.:.yl _ _ _ .. _ h
Transferase
¥ CI
~HCOCH3
TH2CH-COOH
~"
NOz
N0 2
Figure 2.22. Mercapturic acid pathway in mammals.
plants (Lamoureux and Frear, 1979; Shimabukuro et at., 1978a). Insecticides
such as parathion and its O-analog, tetrachlorvinphos, diazinon, and other phosphoric acid triesters are known to be metabolized by glutatione S-transferases in
mammals and insects (Eto, 1974). None of these insecticides has been shown
to be metabolized by GSH conjugation in plants. However, further research may
prove otherwise.
The initial conjugation reaction with GSH occurs in both plants and mammals. However, limited studies with herbicides indicate that, unlike in mammals,
the terminal products in plants may not be mercapturic acids. Atrazine, the first
herbicide reported to be metabolized by GSH conjugation in plants (Lamoureux
et at., 1970), is catabolized to the lanthionine conjugate and other unknown
soluble and insoluble products in sorghum (Fig. 2.23) (Lamoureux et at., 1973;
Shimabukuro et ai., 1973b). The GSH conjugate of atrazine was catabolized to
the S-cysteine conjugate by the sequential loss of glycine and glutamic acid. The
order of amino acid cleavage was the reverse of that in mammals (Fig. 2.22).
The S-cysteine conjugate was not acetylated to yield the mercapturic acid as