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Molecular Forms of Acetylcholinesterase in Bovine Caudate Nucleus and Superior Cervical Ganglion: Solubility Properties and Hydrophobic Character
Author(s) -
Grassi Jacques,
Vigny Marc,
Massoulié Jean
Publication year - 1982
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1982.tb08651.x
Subject(s) - caudate nucleus , acetylcholinesterase , chemistry , monomer , biophysics , nucleus , ganglion , stereochemistry , enzyme , crystallography , biochemistry , anatomy , biology , organic chemistry , neuroscience , polymer
In the present paper, we report an analysis of acetylcholinesterase molecular forms in the bovine caudate nucleus and superior cervical ganglion. We show that: (1) The superior cervical ganglion contains a significant proportion (∼ 15%) of collagen‐tailed forms (mostly A 12 and A 8 ), but these molecules are found only as traces (ca. 0.002%) in the caudate nucleus, even in favorable extraction conditions (i.e., in the presence of 1 m ‐NaCl, 5 m m ‐EDTA, 1% Triton X‐100). (2) The bulk of acetylcholinesterase corresponds to globular forms, mostly the tetrameric G 4 and the monomeric G 1 forms, with a smaller proportion of the dimeric G 2 form. (3) The tetrameric enzyme exists as a minor soluble component (G S 4 ) that does not interact with Triton X‐100, and a major hydrophobic component (G H 4 ) that is partially solubilized in the absence of detergent in the caudate nucleus, but not in the superior cervical ganglion. (4) The monomeric G 1 form presents a marked hydrophobic character, as indicated by its interaction with Triton X‐100, although it may be solubilized in large part in the absence of detergent in both tissues. (5) The detergentsolubilized forms aggregate upon removal of detergent. This property disappears after partial purification of G 4 ) that does not interact with Triton X‐100, and a major hydrophobic component (G H 4 , but is restored upon addition of an inactivated crude extract, indicating that it is attributable to interactions with other hydrophobic components. (6) The proportions of molecular forms solubilized in detergent‐free buffers vary with the ionic composition of the medium. Repeated extractions of caudate nucleus in Tris‐HCl buffer produce a larger overall yield of G 1 form (e.g., 40%) than appears in a single quantitative detergent solubilization (<15%). This G 1 form apparently derives in part from a pool of G H 4 form. (7) However, detergents that allow a quantitative solubilization of acetylcholinesterase yield the same proportions of forms (about 85% G 4 ) independently of the ionic conditions. (8) Modifications of the molecular forms occur spontaneously during purification, or storage of the crude aqueous ex‐tracts, in a manner that depends on the ionic conditions. In Tris‐HCl buffer, G 1 is converted into a well‐defined 7.5S form. In Ringer, polydisperse components are formed. The effects observed in Ringer cannot be reproduced by addition of 5 m m ‐Ca 2‐ to the Tris buffer either during or after extraction. (9) Proteases, such as pronase, convert the hydrophobic forms into molecules that do not appear to interact with Triton X‐100, and do not aggregate in its absence. These results raise fundamental questions regarding the status of acetylcholinesterase in situ , the structure and interactions of its molecular forms. They are discussed with reference to previous publications.