Phosphonylation of purified human, canine and porcine cholinesterase by soman. Stereoselective aspects.
Cholinesterases (EC 3.1.1.8, acylcholine acylhydrolase) from the sera of man, dog and pig were purified 400-600-fold using a combination of ion-exchange and affinity chromatography. In a first approach, phosphonylation by soman was studied by using the half-resolved epimers C(+)P(+/-)-soman and C(-)P(+/-)-soman. The degradation of soman at the nanomolar level was followed in time by determining the remaining soman by capillary gas chromatography with NP detection. In the three sera investigated the P-(-)-epimer phosphonylates at a higher rate than its corresponding P(+)-counterpart and the stereoselectivity is greater for the C(+)-epimers than for the C(-)-epimers. Individual soman isomers were isolated from C(+)- and C(-)-epimers and quantified by gas chromatography. Second-order rate constants were determined for the phosphonylation of purified cholinesterase by isolated soman isomers. The C(+)P(-)-isomer has the highest phosphonylation rate for the three species; the other toxic isomer, C(-)P(-), has a five to ten-fold lower rate. The overall stereoselectivity is more marked in human cholinesterase than in canine. Porcine serum cholinesterase is phosphonylated by the P(-)-isomers at a slightly higher rate than the human enzyme.
De Bisschop
H C
HC
Royal Military Academy, Brussels, Belgium.
Michiels
K W
KW
Vlaminck
L B
LB
Vansteenkiste
S O
SO
Schacht
E H
EH
D000818:Animals; D001665:Binding Sites; D002802:Cholinesterases / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D004285:Dogs; D006801:Humans; D007700:Kinetics; D010758:Phosphorus / Q000378:metabolism*; D012999:Soman / Q000494:pharmacology*; D013237:Stereoisomerism; D013552:Swine
D010758:Phosphorus; D012999:Soman; D002802:Cholinesterases