AFFINITY AND PHOSPHORYLATION CONSTANTS OF OPTICAL ISOMERS OF O,O-DIETHYL MALAOXON AND GEOMETRIC ISOMERS OF PHOSDRIN WITH ACETYLCHOLINESTERASE

The affinity constant (Ka) of the d-isomer of O,O-diethyl malaoxon with acetylcholinesterase at 5° was 2·3(± 0·23) × 10-3M and for the l-isomer 4·9(± 0·51) × 10-3M. The phosphorylation rate (kp) of the d-isomer (63.0 ± 3.2 min-1) was twice that of the l-isomer. Overall, the inhibitory power (ki) was four times greater for the d-isomer than for the l-isomer. With the geometric isomers of Phosdrin, the cis-isomer had a Ka of 1·7 (± 0·06) × 10-3M and the trans-isomer had a Ka of 3·2 (± 0·65) × 10-3M. The kp of the cis-Phosdrin (59·0 ± 1·20 min-1) was ten times that of the trans-isomer. The 20-fold difference in the inhibitory power of the cis-isomer was largely attributed to the difference in the phosphorylation rate. © 1969.