Membrane-bound choline acetyltransferase of the torpedo has characteristics of an integral membrane protein and can be solubilized by proteolysis

Synaptic Soluble and Membrane-Bound Choline Acetyltransferase as a Marker of Cholinergic Function In Vitro and In Vivo

“…ChAT has long been recognized as a cytoplasmic enzyme, even after its detection on synaptic membranes in the 1960s [1,114]. Later, it was shown that ChAT exists as a structural membrane protein [95,[115][116][117]. The long-term study of the properties of synaptic soluble (c) and membrane-bound (m) ChAT in vitro has shown that the relationship between ChAT activity and the secretion of ACh depends on the compartmentalization of the enzyme.…”

“…4-15% [1,94,95,97,119]. Therefore, for a long time, it was assumed that the association of ChAT with neuronal membranes was an artifact as the result of synaptoplasm contamination [1,35,114].It has now been shown that mChAT exists (1) as stationary membrane protein [99,115,117] and (2) as ionic-bound mChAT, a reversible form of cytosolic ChAT [95,126].…”

Effects of Colchicine Application to Preganglionic Axons on Choline Acetyltransferase Activity and Acetylcholine Content and Release in the Superior Cervical Ganglion

“…This association partly depends on a reversible binding that changes according to the ionic milieu (Fonnum, 1968;Fonnum and Malthe-Sørenssen, 1973) and might be controlled by the phosphorylation state of ChAT (Bruce and Hersh, 1989;Schmidt and Rylett, 1993a). Also, a fraction of cellular ChAT is now considered membranous (see, e.g., Smith and Carroll, 1980;Eder-Colli and Amato, 1985;Peng et al, 1986;Salem et al, 1993;Schmidt and Rylett, 1993b); it may be inserted into membranes, removable by proteinase K (Eder-Colli et al, 1992), or held there by a glycosylphosphatidylinositol link (Carroll and Smith, 1990;Smith and Carroll, 1993). The microtubule-dependent transport of ChAT could result from one or both of these membrane associations.…”

“…Between 5 and 18% of total axonal ChAT is transported at fast rates [30-200 mm/day (Dziegielewska et al, 1976)], whereas the remainder moves at slow rates [2-5mmlday 1. These findings are consistent with the idea that a fraction of the axoplasmic ChAT exists in a membrane-bound form, which may associate with microtubules and undergo fast axonal transport, whereas the remainder exists in soluble form in the cytosol and presumably is transported with cytomatrix proteins by slow axonal transport; there is evidence that ChAT exists, in part, as a cytosolic enzyme and, in part, as a membrane-associated one (see, e.g., Fonnum and Malthe-SØrenssen, 1973;Eder-Colli et al, 1992).…”