Daeh N-Terminal Sequence Of Avian Serum Albumins As Catalytic Center Of Cu (Ii)-Dependent Organophosphorus Hydrolyzing A-Esterase Activity

O-hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP) induces delayed neuropathy. The R (+)-HDCP inhibits and caused the so call "aging reaction" on inhibited-NTE. This enantiomer is not hydrolyzed by Ca(II)-dependent A-esterases in mammal tissues but is hydrolyzed by Cu(II)-dependent chicken serum albumin (CSA). With the aim of identifying HDCP hydrolysis by other vertebrate albumins, we incubated albumin with 400 mu M racemic HDCP in the presence of 100 mu M copper sulfate. HDCPase activity was assessed by measurement of HDCP with chiral chromatography. Human, sheep, dog, pig, lamprey or cobra serum albumin did not show a significant activity (-10%). Rabbit and bovine albumins hydrolyzed both enantiomers of HDCP (25% and 50% respectively). Turkey serum albumin had more HDCPase activity (-80 mu M remaining) than the chicken albumin (-150 mu M remaining). No animal albumins other than chicken showed stereoselective hydrolysis. Preincubation of chicken albumin with 1 mM the histidine modifying agents, 100 mu M N-bromosuccinimide (NBS) and Zn(II), inhibited its Cu(II)-dependent R (+)-HDCPase activity, where as other mM amino acids modifiers had no inhibitory effects. . These results confirm that the stereoselective hydrolysis of (+)-HDCP is a specific A-esterase catalytic property of chicken albumin. The higher HDCPase activity by turkey albumin suggests the aminoterminal sequence of avian albumins (DAEHK) is the active center of this Cu(II)-dependent A-esterase activity.