ARYL ACYLAMIDASE ACTIVITY EXHIBITED BY BUTYRYLCHOLINESTERASE IS HIGHER IN CHICK THAN IN HORSE, BUT MUCH LOWER THAN IN FETAL CALF SERUM

Several side activities have been attributed to butyrylcholinesterase (BChE), including aryl acylamidase (AAA) activity, which is an amidase -like activity with unknown physiological function splitting the artif icial substrate o-nitroacetanilide. For avians, extensive developmenta l data have pointed to neurogenetic functions of BChE, however, a poss ible AAA activity of BChE has not been studied. In this study, we firs t compare the relative levels of AAA exhibited by BChE in whole sera f rom chick, fetal calves (FCS) and horse. Remarkably, FCS exhibits a 40 0-fold higher ratio of AAA/BChE than horse and 80-fold higher than chi ck serum. We then show that an immunoisolated preparation of BChE from chicken serum presents significant activity for AAA. Both in sera and with the purified enzyme, the AAA activity is fully inhibited by anti cholinesterase drugs, showing that AAA activity is exclusively conveye d by the BChE molecule. Noticeably, AAA inhibition even occurs at lowe r drug concentrations than that of BChE activity itself. Moreover, AAA is sensitive to serotonin. These data indicate that (1) AAA is a gene ral feature of serum BChE of vertebrates including avians, (2) AAA is effectively inhibited by cholinergic and serotonergic agents, and (3) AAA may have a developmental role, since it is much pronounced in a se rum from fetal animals. Functionally, deamination of neuropeptides, a link between cholinergic and serotonergic neurotransmitter systems, an d roles in lipoprotein metabolism could be relevant. (C) 1998 Publishe d by Elsevier Science Ireland Ltd. All rights reserved.