Aryl acylamidase activity on acetylcholinesterase is high during early chicken brain development

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are known to exhibit aryl acylamidase activities (here called AAA(AChE) and AAA(BChE), respectively), which have been suggested to be involved in developmental and pathological processes. We here have investigated the developmental profiles of both AAA(AChE) and AAA(BChE) activities along with their AChE and BChE activities from embryonic days E3 to hatching (E21) in Triton-extracted homogenates from chicken embryonic brains. AAA(AChE) follows continuously an increase that is typical for AChE expression itself, whereas AAA(BChE) was relatively high before E10 to then become negligible toward hatching. Sucrose gradient centrifugation of both homogenized and immunopurified samples from E6-E18 brains showed that all globular forms (G1, G2, G4) of AChE present AAA(AChE) activity. Interestingly, the ratio of AAA(AChE) to AChE is highest at E6, and here again higher on G1/G2- over the G4-form. Noticeably, the sensitivity of AAA(AChE) toward the specific AChE inhibitor BW284c51 at all stages is higher than that of AChE itself. These data of high ratios of AAA associated at young stages with cholinesterases strongly indicate a role of AAA in early brain development.