Molecular Forms Of Acetylcholinesterase Research Articles

Asymmetric and globular forms of acetylcholinesterase in mammals and birds.

We have identified six molecular forms of acetylcholinesterase (AcChoE: acetylcholine hydrolase, EC 3.1.1.7) in extracts from bovine superior cervical ganglia. We show that three of them resemble the collagen-tailed forms of Electrophorus AcChoE in their hydrodynamic parameters, low-salt aggregation properties, and collagenase sensitivity. The six molecular forms of bovine AcChoE appear structurally homologous to the six forms of electric fish AcChoE that have previously been characterized. They include globular molecules (monomers, dimers, and tetramers) and asymmetric aggregating molecules that possess a collagen-like tail associated with one, two, and three tetramers. We propose to call the globular forms G1, G2, and G4 and the asymmetric forms A4, A8, and A12, the subscripts indicating the number of catalytic subunits. In spite of quantitative differences in their molecular parameters, the AcChoE forms from rat and chicken are clearly homologous to those of bovine AcChoE. Thus the nomenclature we introduce is very probably valid for the main AcChoE molecular forms, at least in vertebrates, and should help to clarify structural relationships and homologies among them. This model, however, does not claim to represent entirely the complex polymorphism of AcChoE, because more or less hydrophobic variants of the G forms have been observed, and because other molecular associations cannot be excluded. We discuss the significance of the globular and collagen-tailed structure for the molecular localization of AcChoE.

Distribution of acetylcholinesterase molecular forms in neural and non-neural sections of human muscle

Distribution of acetylcholinesterase molecular forms in neural and non-neural sections of human muscle

Effect of denervation on the molecular forms of acetylcholinesterase in normal and dystrophic chicken muscles

Effect of denervation on the molecular forms of acetylcholinesterase in normal and dystrophic chicken muscles

Molecular forms of acetylcholinesterase in the ciliary ganglion and iris of the chick. Developmental changes and effects of axotomy.

Four molecular forms of acetylcholinesterase (AChE) have been observed in extracts from ciliary ganglion and iris by gel electrophoresis followed by Koelle's reaction and densitometry on gels. Forms I, II, and III (order of anodic migration) are present in the 'soluble fraction' (SF) while forms II, III, and IV appear in the 'membranous fraction' (MF). 10 days after postganglionic axotomy in young chickens, the relative proportions of the membranous forms were changed in both the ciliary ganglion and iris, with a marked reduction of form IV occurring. A characteristic evolution of both the soluble and membranous forms of AChE was evident through different developmental stages (10th day of incubation; 2nd, 11th and 56th day posthatching). In the ciliary ganglion the faster components were reduced in favor of form IV. Conversely, the relative proportion of the faster components was increased in the iris. The observed changes in the AChE forms are compared with changes in the structure and function of these organs known to occur in the conditions under study. Evidence is presented which suggests a junctional localization for the form IV in both the ciliary ganglion and iris.

Rapid accumulation of high molecular weight acetylcholinesterase in transected sciatic nerve.

NERVOUS tissue and muscle in rat1–4 and chicken5,6 contain several molecular forms of acetylcholinesterase (EC 3.1.17, AChE), distinguishable by their sedimentation coefficient in sucrose gradient7. In rat, several peripheral nerves and non-innervated regions of skeletal muscle1,2 were shown to contain two molecular forms of AChE, with respective sedimentation coefficients of 4 and 10S; in addition to these two forms, a high molecular weight form with a sedimentation coefficient of 16S was found in the innervated regions of various skeletal muscles1,2,4. After denervation, the 16S form, which we will call the H form, either disappeared from skeletal muscle2 or was drastically reduced1,4. In chicken, several nerves exhibited three molecular forms of AChE with sedimentation coefficients of 4, 6.5 and 11S, while various skeletal muscles contained an additional molecular form with a sedimentation coefficient of 19.5S (ref. 5). After denervation, the high molecular weight form 19.5S, which by analogy with the 16S of rat is referred to here as the H form, disappeared from crude extract of muscles5. As the H form was only found in tissues innervated by cholinergic nerve endings and disappeared or decreased drastically from denervated skeletal muscles, it has been suggested that this form of AChE is exclusively myogenic1,3 and may constitute the specific endplate enzyme1,2,4,5. We report here that tiny amounts of the H form of AChE can be detected in crude extracts of intact sciatic nerves of rat and chicken, and that after transection of the sciatic nerve with the ensuing blockade of the axonal traffic, the H form increased rapidly at the site of injury.

Molecular forms of acetylcholinesterase from Torpedo californica: their relation to synaptic membranes

The 16S and 8S forms of acetylcholinesterase (AchE), which are composed of an elongated tail structure in addition to the more globular catalytic subunits, were extracted and purified from membranes from Torpedo californica electric organs. Their subunit compositions and quaternary structures were compared with 11S lytic enzyme which is derived from collagenase or trypsin treatment of the membranes and devoid of the tail unit. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the absence of reducing agent, appreciable populations of monomeric through tetrameric species are observed for the 11S form. Under the same conditions, the 16S form yields only monomer and dimer in addition to a higher molecular weight species. If complete reduction is effected, only the 80,000 molecular weight monomer is dominant for both the 11S and 16S forms. Cross-linking of the 11S form by dimethyl suberimidate followed by reduction yields monomer through tetramer in descending frequency, while the 16S form again shows a high molecular weight species. A comparison of the composition of the 11S and 16S forms reveals that the latter has an increased glycine content, and 1.1 and 0.3 mol % hydroxyproline and hydroxylysine, respectively. Collagenases that have been purified to homogencity and are devoid of amidase and caseinolytic activity, but active against native collagen, will convert 16S acetylcholinesterase to the 11S form. Thus, composition and substrate behavior of the 16S enzyme are indicative of the tail unit containing a collagen-like sequence. A membrane fraction enriched in acetylcholinesterase and components of basement membrane can be separated from the major portion of the membrane protein. The 16S but not the 11S form reassociates selectively with this membrane fraction. These findings reveal distinct similarities between the tail unit of acetylcholinesterase and basement membrane components and suggest a primary association of AchE with the basement membrane.

Electron microscopic studies on stretched and globular acetylcholinesterase molecules of the electric eel (Electrophorus electricus)

Electron micrographs of the various molecular forms of acetylcholinesterase (as previously characterized) are presented. The “globular” forms G and G' appear as tetramers, and dimers, respectively, whereas the “native” forms, A, C, and D show a structure “en grappe” where a cluster of globules (respectively 4, 6 to 8, and at least 10) is associated with a semi‐rigid “tail”. The globules seem identical in all forms and probably represent the sub‐units of the enzyme (Mw 60000—80000). The structures are 50 nm long in their greatest dimension; the tail is 2—3 nm thick and its visible part is longest in A and shortest in D; presumably part of it is masked by the head. These results explain our previous physico‐chemical observations which had led us to propose that the native forms were asymmetric in structure. We discuss a possible model of the sub‐unit structure for the “native” forms: A, C and D are proposed to consist of identical tails associated with respectively one, two, and three tetramers. This hypothesis provides a rationale for the occurrence of three well‐defined “native” acetylcholinesterases, as well as for the derived “globular” forms, the dimer and the tetramer. We further propose that the interactions inside the structures are not equivalent for the two kinds of subunits: for example, one of them might be linked directly to the tail, the other only through the tetramer interactions.

Histochemical, biochemical, and contractile properties of red, white, and intermediate fibers.

Histochemical, biochemical, and contractile properties of red, white, and intermediate fibers.