Studies on choline acetyltransferase isolated from human brain

Choline and cholinergic neurons

Mammalian neurons can synthesize choline by methylating phosphatidylethanolamine and hydrolyzing the resulting phosphatidylcholine. This process is stimulated by catecholamines. The phosphatidylethanolamine is synthesized in part from phosphatidylserine; hence the amino acids methionine (acting after conversion to S-adenosylmethionine) and serine can be the ultimate precursors of choline. Brain choline concentrations are generally higher than plasma concentrations, but depend on plasma concentrations because of the kinetic characteristics of the blood-brain-barrier transport system. When cholinergic neurons are activated, acetylcholine release can be enhanced by treatments that increase plasma choline (for example, consumption of certain foods).

Purification and immunochemical properties of choline acetyltransferase from human brain

Choline acetyltransferase (CAT) was purified to homogeneity from 363 g of human neostriatum by means of ammonium sulfate and protamine sulfate fractionation, followed by chromatography on DEAE-Sephadex, hydroxyapatite, phosphocellulose, and agarose-hexane-Co A columns. The final product migrated as a single component on 7.5% gels with or without SDS. It had a molecular weight of 66,000 daltons and a specific activity of 7.3 mumol acetylcholine formed per milligram protein per minute. Antibodies prepared in rabbits gave single precipitin lines against this protein on Ouchterlony immunodiffusion and immunoelectrophoresis plates. The CAT-anti-CAT IgG complex migrated as a single band on gel electrophoresis, establishing the monospecificity of the antibodies. Strong cross-reactivity to the IgG was obtained with CAT from rat, rabbit, and guinea pig, but only weak reactivity with chicken. Fab fragments were prepared from the rabbit IgG and were used to stain CAT-containing neurons in the spinal cord and nerve endings at the neuromuscular junction using the PAP technique.

Cholinergic systems in muscle and brain in vitamin E-deficient rats

Rats fed a vitamin E-deficient diet for 7--8 weeks postweaning showed no change in brain weight or the activity in brain of various enzymes involved in neurotransmitter synthesis and metabolism. Body and muscle weights were markedly reduced. Muscle choline acetyltransferase and acetylcholinesterase activities were significantly elevated on a protein basis, but the total amount of choline acetyltransferase/muscle was essentially normal and total acetylcholinesterase activity was slightly reduced. Total carnitine acetyltransferase and butyrylcholinesterase activities were markedly decreased. The results are quite different from those found in hereditary murine muscular dystrophy and suggest a myogenic etiology for the vitamin E-deficiency-induced condition.

Choline acetyltransferase and acetylcholinesterase in muscular dystrophic mice

The activities of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were assayed in various tissues of dystrophic (dy/dy) and normal mice of Bar Harbor strain 129. The brain weights of these dystrophic mice were not significantly different from those of normal mice, but the average body weight of these dystrophic mice was only 66.8% of that of the controls. The activity of CAT (expressed as unit activity per mg of protein) was very similar in the brains of both groups of animals, but the CAT activity (per mg of protein) in the hindlimb muscles of the dystrophic mice was significantly higher than that of the controls. The patterns of AChE activity, as separated by sucrose density gradient centrifugation, were distinctly different in extracts of dystrophic and normal muscle. Compared with controls, decreased activity of the 15-S and 10-S forms of AChE, with increased activity of a 4.3-S formed of AChE, was observed in dystrophic muscle.