Active Site and Other Sequence Data from Torpedo Californica Acetylcholinesterase

Abstract

Two distinct molecular forms of acetylcholinesterase are found in the electric organ of Torpedo californica: a dimensionally asymmetric species localized in the basal lamina of the synapse and a globular, hydrophobic species associated with the plasma membrane (1–3). The asymmetric species are; comprised of two or usually three tetrametric sets of catalytic subunits linked to both collagenous and non–collagenous structural subunits. These elongated species sediment as discrete 13S and 17S species respectively and as an 11S species after limited proteolytic treatment (4–6). The hydrophobic globular species is a dimer of catalytic subunits with a sedimentation constant of 5.6S in the presence of a neutral detergent. The catalytic subunits of these two forms exhibit small differences in electrophoretic migration, amino acid composition, monoclonal antibody affinity, and peptide mapping (3,4,7). Primary structural studies were undertaken in order to define specific functional sites and, in addition, to elucidate whether the observed structural differences between the two acetylcholinesterase species are the result of multiple genes, alternate mRNA transcripts, or post–translational modifications.