Heparin and the solubilization of asymmetric acetylcholinesterase

Abstract

Heparin solubilizes asymmetric acetylcholinesterase, from chick skeletal muscle and retina, as a 24 S complex which is quantitatively converted to conventional asymmetric molecular forms of the enzyme (A,, and As, either class I or class II) upon exposure to high salt. The simultaneous presence of salt and heparin in the homogenization medium selectively prevents, however, the release of class II A-forms in both muscle and retina. Heparin may generally act by displacing native proteoglycans involved in the attachment of the enzyme tail to the extracellular matrix, or its neural equivalent, being in turn removed by salt to yield typical asymmetric enzyme forms. Heparin would also appear to displace some other molecules specifically involved in the EDTA-sensitive attachment of class II tailed forms, this effect being antagonized by salt.Acetylcholinesterase Heparin EDTA

Chondroitinases release acetylcholinesterase from chick skeletal muscle

“…Among glycosaminoglycans (GAGS), heparan sulfate has been singled out as the most likely candidate for this role in view of the proven affinity of the tailed AChE species for heparin [3][4][5][6]8], and of the reported ability of heparinases (but not chondroitinases) to dissociate aggregative AChE-GAG complexes [2], and to release asymmetric AChE from electric organ samples [S]. Our recent work has shown, however, that the affinity of heparin for the asymmetric AChE tail is not a selective phenomenon, being shared by a number of polyanions including sulfated GAGS, dextran sulfates, some acidic polyaminoacids and even polyvinylsulfates [9].…”

“…Experimental evidence has a.ccumulated during recent years which supports the involvement of the glycosaminoglycan moiety of proteoglycans in the anchorage of the asymmetric, collagen-tailed forms (Aforms) of acetylcholinesterase (AChE; EC 3.1.1.7) to the basal lamina, at the motor endplate, in vertebrate skeletal muscle [l-8]. Among glycosaminoglycans (GAGS), heparan sulfate has been singled out as the most likely candidate for this role in view of the proven affinity of the tailed AChE species for heparin [3][4][5][6]8], and of the reported ability of heparinases (but not chondroitinases) to dissociate aggregative AChE-GAG complexes [2], and to release asymmetric AChE from electric organ samples [S]. Our recent work has shown, however, that the affinity of heparin for the asymmetric AChE tail is not a selective phenomenon, being shared by a number of polyanions including sulfated GAGS, dextran sulfates, some acidic polyaminoacids and even polyvinylsulfates [9].…”

Transient Interactions between Collagen-tailed Acetylcholinesterase and Sulfated Proteoglycans Prior to Immobilization on the Extracellular Matrix

“…A likely candidate molecule involved in localizing AChE to the neuromuscular junction is a heparan sulfate proteoglycan (HSP). A 12 AChE binds specifically to heparin and sulfated glycosaminoglycans (Bon et al, 1978;Vigny et al, 1983;Brandan et al, 1985;Brandan and Inestrosa, 1986) and can be solubilized from muscle with heparin ; Barat et al, 1986) or other polyanions (Pérez-Tur et al, 1991a). Electron microscopy of negatively stained aggregates of A 12 AChE and polyanionic components of the extracellular matrix from Torpedo electric organs shows that the distal regions of the collagen-like tail are involved in the binding (Bon et al, 1978).…”

Compartmentalization of acetylcholinesterase in the chick retina

“…Although the CNS does not contain basal laminae as such, the extracellular matrix-like material making up the synaptic cleft does contain GAGS and may provide anchorage points for the collagen-like tails of asymmetric AChE (Buckley et al, 1983). Actually, we have been able to solubilize A-forms, from chick retina, by means of heparin, with an extraction efficiency similar to that observed in "peripheral" tissues (Barat et al, 1986).…”

“…and H.L.F.). Barat et al, 1986). Although the CNS does not contain basal laminae as such, the extracellular matrix-like material making up the synaptic cleft does contain GAGS and may provide anchorage points for the collagen-like tails of asymmetric AChE (Buckley et al, 1983).…”