Monroy-Noyola_2018_Food.Chem.Toxicol_120_523

O-hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP) is a chiral analogous compound of the methamidophos insecticide that induces delayed neuropathy, and the R-(+)-HDCP enantiomer is an inhibitor of neuropathy target esterase (NTE). This enantiomer is not hydrolized by Ca(2+)-dependent phosphotriesterases in mammal tissues. Our group had reported R-(+)-HDCP hydrolysis in chicken serum enhanced by 30-250 muM copper in ex vivo assays, which we call "antagonistic stereoselectivity". We checked the hypothesis of the role of cupper binding proteins. Two hundred micrograms of human serum ceruloplasmine or horse kidney methallotionein in 1mL containing 400muM HDCP for 60min showed no significant Cu(2+)-dependent hydrolysis. However under the same conditions, 10muL of chicken serum or 10muL of buffer containing 216mug of chicken serum albumin (CSA) (amount of albumin content in this serum volume) with 100muM Cu(2+) showed the same stereoselectivity and similar levels to the Cu(2+)-dependent R-(+)-HDCP hydrolysis. About 75% of R-(+)-HDCP were hydrolyzed after 120 min in the presence of 100 muM Cu(2+) (inhibited by 5mM EDTA). No effects was observed by divalent cations Cu(2+), Zn(2+), Fe(2+), Ca(2+), Mn(2+) and Mg(2+). These results confirm that albumin is the protein responsible for "antagonistic stereoselectivity" observed in chicken serum.