Activity of Carboxylesterase Toward Malathions 

Kn* SE V max + SE Relative enzy- 
(mM) uM/mg/min matic half-life 
0.695 (K/V,) 
d -Malathion 0.084 + 0.007 0.761 + 0.011 0.077 
1 -Malathion 0.159 + 0.008 0.559 + 0.008 0.218 
dl-Malathion 0.205 + 0.008 0.937 + 0.043 0.152 

Bimolecular Reaction Constants of Malaoxons 
k, x 104(m~! min 71) 
Bovine erythrocyte 
AcCh Rat Liver 
a __ esterase carboxy lesterase 
d -Malaoxon 2.80 5.40 
1 -Malaoxon 0.63 0.65 
dl-Malaoxon 1.49 Le70 
(1673) 
Studies with the optically active isomers of malathion and malaoxon 
showed that the d-isomer was more toxic that the l-isomer (1673). 
232 
