Electric eel acetylcholinesterase: a multisubunit enzyme containing a collagen tail.

Molecular forms of acetylcholinesterase (AChE) in fresh electric organ tissue are elongated structures in which a multisubunit head containing the catalytic sites is attached to a fibrous tail. The principal form, 18S AChE, is of MW ca. 1,100,000 and aggregates reversibly at low ionic strength. Trypsin converts it to an 11S globular tetramer devoid of the tail and lacking the capacity to aggregate reversibly in low salt. Amino acid analysis, collagenase and pepsin digestion and immunological techniques were utilized to demonstrate that the fibrous tail of the elongated forms of AChE is a collagen triple helix. The distal portion of the tail contains a region responsible for the capacity for aggregation at low ionic strength. This latter property may be related to the postulated role of the tail in anchoring AChE to the fibrillar matrix of the basal lamina.