Some properties of isozymes of brain acetylcholinesterase

HISTONE REGULATION OF LACTIC DEHYDROGENASE IN EMBRYONIC CHICK BRAIN TISSUE

Histone, when added at low concentrations to cultures of embryonic chick brain tissue, causes an inductive response in lactic dehydrogenase activity, whereas at higher concentrations of histone the response is repressive. This control is shown to operate by altering protein synthesis. Thus, histones exercise a primary regulatory function in the chick. Unlike lactic dehydrogenase, acetylcholine esterase is stable in this system and is not affected by histones or inhibitors of protein synthesis.

Study of the structuro-catalytic peculiarities of brain acetylcholinesterase in the postnatal ontogenesis of rabbits

The structuro-catalytic peculiarities of acetylcholinesterase (AChE) of the cerebral hemisphere of newborn, month-old, and adult rabbits were investigated. In the process of individual development, no changes were detected in the structure of the active surface of the enzyme, but differences were detected in the macromolecular organization and sensitivity to allosteric ligands. A hypothesis was advanced on the complication of the structural organization of AChE during postnatal ontogenesis. providing the possibility of the finest regulation of its activity.

Isoenzymes of soluble and membrane-bound acetylcholinesterase in boine splanchnic nerve and adrenal medulla

Centrifugation of homogenates of bovine splanchnic nerve trunks and adrenal medulla showed that 47% and 31%, respectively, of the acetylcholinesterase activity was not sedimentable. The possibility that the soluble acetylcholinesterase activity was derived artefactually from the membrane-bound form was excluded. Gel electrophoresis revealed that the soluble acetylcholinesterase activity in adrenal medulla was distributed between five isoenzymes, only one of which was found in the supernatant fraction of splanchnic nerve homogenates. Solubilization of the membranes of both tissues with Triton X-100 gave a single isoenzyme of acetylcholinesterase, common to both tissues, whose electrophoretic mobility was less than that of any of the soluble isoenzymes. Some of the properties of the soluble and membrane-bound isoenzymes of acetylcholinesterase of splanchnic nerve were compared: the Michaelis constants were identical, both isoenzymes sedimented to the same position as catalase (molecular mass 240 000) in a density gradient, their mobilities varied in a parallel fashion upon electrophoresis in gels of different concentration. It was concluded that the higher electrophoretic mobility of the soluble isoenzyme was because it carried a greater charge than, but had a similar molecular mass to, the membrane-bound isoenzyme.

Analysis of the forms of acetylcholinesterase from adult mouse brain

The solubilization of 80% of the acetylcholinesterase activity of mouse brain was performed by repeated 2h incubations of homogenates at 37 degrees C in an aqueous medium. Analysis of the soluble extract by gel filtration on Sephadex G-200 showed that up to 80% of the enzyme activity was eluted in a peak which was estimated to consist of molecules of about 74000mol.wt. This peak was called the monomer form of the enzyme. After 3 days at 4 degrees C, the soluble extract was re-analysed and was eluted from the column in four peaks of about 74000, 155000, 360000 and 720000 mol.wt. Since the total activity of the enzyme in these peaks was the same as that in the predominantly monomer elution profile of fresh enzyme, we concluded that the monomer had aggregated, possibly into dimers, tetramers and octomers. Extracts of the enzyme were analysed by polyacrylamide-gel electrophoresis and the resulting multiple bands of enzyme activity on gels were shown to separate according to their molecular sizes, that is by molecular sieving. All these forms had similar susceptibilities to the inhibitors eserine, tetra-isopropyl pyrophosphoramide and compound BW 284c51 [1,5-bis-(4-allyldimethylammoniumphenyl)pentan-3-one dibromide]. Thus the forms of the enzyme in mouse brain which can be detected by gel filtration and polyacrylamide-gel electrophoresis may all be related to a single low-molecular-weight form which aggregates during storage. This supports similar suggestions made for the enzyme in other locations.

Multiple forms of acetylcholinesterase from pig brain

1. A number of methods of solubilization of pig brain acetylcholinesterase (EC 3.1.1.7) were studied. The multiple enzymic forms of the resultant preparations were examined by polyacrylamide-gel electrophoresis. 2. Butanol extraction, Nagarase treatment and ultrasonication proved unsuitable as preparatory methods, but detergent treatment (Triton X-100, Triton X-100-KCl and lysolecithin) gave good yields. 3. Separation of soluble enzyme in three systems of polyacrylamide-gel electrophoresis were compared and the relative advantages are discussed. 4. By using a 6% (w/v) gel and continuous buffer system two forms of acetylcholinesterase were detected in Triton X-100-solubilized enzyme, but the incorporation of a sample and spacer gel and a discontinuous buffer system resolved this into four components. The forms of the soluble enzyme extracted by different methods differed in mobility. 5. With gradient polyacrylamide-gel electrophoresis between two and six forms were detected, depending on the method used for extraction. The average molecular weights of the five forms most frequently found were 60000, 130000, 198000, 266000 and 350000. 6. Treatment of the Triton X-100-extracted enzyme with 2.5m-urea altered the pattern and evidence of dissociation was observed. 7. The results are discussed in the light of present theories on the molecular structure of acetylcholinesterase.

Functional significance of isoenzymes in thermal acclimatization. Acetylcholinesterase from trout brain

1. The effects of acclimatization temperature on the catalytic properties of acetylcholinesterase from rainbow-trout brain were examined. 2. Trout brain acetylcholinesterase occurs in two distinct forms. A single ;warm' variant of the enzyme is present after acclimatization to 17 degrees C; a single ;cold' variant appears after acclimatization to 2 degrees C. Both forms are present in fish after acclimatization to an intermediate temperature. 3. The K(m) values of the enzyme variants for acetylcholine are temperature-dependent, the lowest values coinciding with the acclimatization temperature at which each enzyme was induced. 4. It is concluded that the K(m)-temperature relationship is adaptive, and that the critical process during thermal acclimatization, in cases where enzymes show sharp changes in K(m) with temperature, is the synthesis of a new enzyme variant that is better suited for catalysis and control of catalysis under the conditions of the acclimatized state.