Novel Inactive and Distinctively Glycosylated Forms of Butyrylcholinesterase from Chicken Serum


Address correspondence and reprint requests to Prof. P. G. Layer at Technische Hochschule Darmstadt, Institut für Zoologie, Darmstadt, F.R.G.


Abstract: Three different homologues of butyrylcholinesterase (BChE) with 75-, 62-, and 54-kDa subunit size are isolated from adult chicken serum, and all show very low or zero enzyme activity. Although the active BChE from serum with a subunit size of 81 kDa forms tetramers, the 75-kDa protein is isolated as a dimer. The homology of the 75-kDa protein with active BChE is shown by immunoreactivity with BChE-specific monoclonal antibodies, by coisolation with the active BChE, and by their identical first six N-terminal amino acids. By deglycosylation of these proteins and by their differential lectin binding, we show that the active BChE is an N-glycosylated protein of the triantennary type, whereas the inactive 75-kDa protein is O-glycosylated. These data show for the first time the existence of (1) multiple inactive forms of BChE, (2) secreted inactive cholinesterases, because they are found in serum, and (3) an O-glycosylated cholinesterase. Because cholinesterases can regulate neurite growth in vitro by a nonenzymatic mechanism, these data strongly support that both inactive and active forms of BChE may be involved in noncholinergic communication, possibly depending on particular glycosylation patterns.