The carbohydrate epitope HNK-1 is present on all inactive, but not on all active forms of chicken butyrylcholinesterase.

The HNK-1 epitope as a hallmark of many cell adhesion molecules is supposed to convey positive cellular interactions. Here, we report that in the adult chick the HNK-1 epitope is absent from active serum butyrylcholinesterases (BChE), but is strongly expressed on all inactive serum BChEs and on active brain BChE. These data further support roles of cholinesterases in cell adhesion, particularly so for their inactive forms. Moreover, we show that the HNK-1-positive BChEs belong to different types of glycoproteins.