Effect of some metallic cations and organic compounds on the O-hexyl O-2,5-dichlorophenyl phosphoramidate hydrolysing activity in hen plasma.
One of the main detoxification mechanisms of organophosphorus (OP) compounds is hydrolysis by OP hydrolysing enzymes (OP-hydrolases) or phosphoric triester hydrolases. We previously reported an OP-hydrolase from hen plasma which hydrolyses O-hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP). In this study, a total of 18 cations, as well as several thiol blocking reagents, ethylenediaminetetraacetic acid (EDTA) and mipafox (N,N'-diisopropyl phosphorodiamidofluoridate) were assayed as activators or inhibitors of the HDCP hydrolysing activity of hen plasma in vitro. Of the 18 inorganic cations only 1 M Na+ caused any inhibition. Most of the cations, including Ca2+, exerted no detectable effect; however, 1 mM Cu2+ was found to produce an activation of up to 263%, with a lesser activation of up to 168% for 1 mM Zn2+. The thiol blocking reagents methyl vinyl ketone (MVK) and N-ethylmaleimide (NEM) inhibited the enzyme in a time-dependent manner, the maximum effect depending upon concentration in the case of NEM, but not in the case of MVK; however, 5,5'-dithiobis (2-nitrobenzoic acid) caused inhibition that was concentration dependent but which was independent of time. Other thiol blocking reagents such as p-hydroxymercuribenzoic acid (sodium salt), phenylmercuric acetate, iodoacetic acid (sodium salt) and iodoacetamide produced only slight inhibition, as did EDTA. Finally, the OP compound mipafox exerted no detectable effect.
Sogorb
M A
MA
Department of Neurochemistry, University of Alicante, Spain.
Díaz-Alejo
N
N
Vilanova
E
E
Vicedo
J L
JL
Carrera
V
V
D000818:Animals; D043303:Aryldialkylphosphatase; D002074:Butanones / Q000494:pharmacology; D002151:Calorimetry; D002412:Cations / Q000494:pharmacology; D002645:Chickens; D003300:Copper / Q000494:pharmacology; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D006867:Hydrolases / Q000037:antagonists & inhibitors* / Q000097:blood*; D006868:Hydrolysis; D007700:Kinetics; D008670:Metals / Q000494:pharmacology*; D009943:Organophosphorus Compounds / Q000097:blood; D010744:Phosphoric Monoester Hydrolases / Q000097:blood; D015032:Zinc / Q000494:pharmacology
D002074:Butanones; D002412:Cations; D008670:Metals; D009943:Organophosphorus Compounds; C066606:hexyl 2,5-dichlorophenylphosphoroamidate; D003300:Copper; D004228:Dithionitrobenzoic Acid; D004492:Edetic Acid; C057920:3-buten-2-one; D006867:Hydrolases; D010744:Phosphoric Monoester Hydrolases; D043303:Aryldialkylphosphatase; D015032:Zinc; D005033:Ethylmaleimide