Molecular Forms of Electrophorus Acetylcholinesterase

Abstract

Molecular weights for the series of six Electrophorus acetylcholinesterase forms have been determined either by the sedimentation‐diffusion equilibrium method or, particularly in the case of the very scarce G′ and G″ forms, from their Stokes radius and sedimentation coefficient values. Both methods are in excellent agreement. The results provide good evidence for the model previously proposed, G″, G′ and G containing one, two and four subunits, whereas A, C and D possess, in addition to respectively one, two and three tetrameric sets of such subunits, a structural element, the tail. Although the amino acid composition of ‘tailed’ and globular forms did not reveal any significant feature of this element, its mass, about 100000 daltons, could be deduced from a comparison of molecular weights for the two classes of acetylcholinesterase forms. This value is in close agreement with electron microscopic data. The tail is thought to consist of three 30000‐dalton strands.

Molecular forms of Electrophorus acetylcholinesterase the catalytic subunits: fragmentation, intra‐ and inter‐subunit disulfide bonds

“…Electron micrographs [5,6] have shown that the asymmetric forms contain a rod-like structure, the 'tail'. We have deduced the number of catalytic subunits from molecular weight data for all forms [7], confirming a model previously proposed [5,6] according to which A, C, D are composed, in addition to a rod like 'tail', of one, two and three tetramers respectively. The forms G, G' and G" are tetramers, dimers and monomers.…”

“…No specific band, either proteic or glycoproteic, could be assigned to the tail of the asymmetric forms. Electron microscopy [6] and molecular weight data [7] have indicated that the tail may consist of three 30 000 dalton chains. When the asymmetric forms were analyzed without reduction, no 30 000 dalton band was visible: it may be that the three tail chains were linked together by disulfide bridges and cofncided in the gel with the monomeric band or, alternately, that they were linked to the catalytic subunits via disulfide bridges.…”

Acetylcholinesterase from human erythrocyte membranes: dimers as functional units

“…It should be noted that these methods do not permit the calculation of the protein frictional ratio from the M r and the sedimentation coefficient of the protein-detergent complex. Thus, it is not possible to decide whether dimeric human erythrocyte membrane acetylcholinesterase is an asymmetric or a globular enzyme form [13].…”

The Dependence of Acetylcholinesterase Aggregation at Low Ionic Strength upon a Polyanionic Component

“…Stokes' radii were determined by molecular sieve chromatography (Biogel A 15 m) for A, C and D forms, as described in [5] and [9]. In the case of the aggregates, a Biogel A 50 m column was used (height 90 cm, diameter 1.5 cm).…”