O-hexyl O-2,5-dichlorophenyl phosphoramidate as a substrate for domestic and sea bird serum A-esterases: Hydrolysis levels, Cu2+- and Zn2+-dependence and stereoselectivity.

O-Hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP) induces delayed neuropathy in hens. It has been used as a tool to identify new A-esterase activities in animal tissues. This study shows the EDTA-resistant, Cu2+- and Zn2+-dependent hydrolysis of racemic HDCP in domestic and sea bird serum using UV/Vis spectrophotometry and chiral chromatography. The results clearly show a significant (p ˂ 0.05) Cu2+- and Zn2+-dependent HDCP hydrolysis in the serum of all bird species versus EDTA, except for the Zn2+-dependent HDCPase activity from Yucatecan quail serum. The ratio of Cu2+/Zn2+ hydrolysis varied between 1 and 7 (intraspecies) and 15.6 (interspecies). EDTA affected the Cu2+- and Zn2+-dependent HDCPase activity in the range of 37-95% and 40-50%, respectively. HDCP hydrolysis activated by Cu2+ was significantly (p ˂ 0.05) stereoselective (R-(+)-HDCP ˃ S-(-)-HDCP) in chicken and sea bird serum. Its R-(+)-HDCP/S-(-)-HDCP ratios were 6.8 and 1.6-2.8, respectively. EDTA-resistant and zinc-dependent HDCP hydrolysis were not stereospecific in all bird sera tested. The present ex vivo study reinforces the idea that bird sera have HDCPase activity that is sensitive to divalent metals, resistant to EDTA and possibly associated with the protein albumin.