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Choline acetyltransferase-like activity bound to neuronal plasma membranes
R Massarelli1, B Ferret, G Sorrentino
1Centre de Neurochimie du C.N.R.S., Strasbourg, France.
Neurochemical Research
|December 1, 1988
Summary
Researchers identified a bound form of choline acetyltransferase (CAT) in rat brain membranes. This enzyme synthesizes acetylcholine and exhibits distinct properties from its soluble counterpart.
Area of Science:
- Neuroscience
- Biochemistry
Background:
- Choline acetyltransferase (CAT) is crucial for acetylcholine synthesis.
- The localization and properties of membrane-bound CAT are not fully understood.
Purpose of the Study:
- To characterize the membrane-bound form of CAT in rat brain synaptosomes.
- To investigate the synthesis and release of acetylcholine from intact neuronal preparations.
Main Methods:
- Enzyme activity assays using synaptosomal membranes and Triton X-114 extraction.
- Kinetic analysis (Km values for choline and AcCoA).
- Isoelectric focusing to determine enzyme isoforms.
- Experiments with intact synaptosomes and PC 12 cells using radioactive substrates.
Main Results:
- A CAT-like activity was found in rat brain synaptosomal membranes, separable by Triton X-114.
- The bound enzyme showed pH optimum of 8, NaCl activation, and specific inhibition patterns.
- Kinetic parameters (Km) for choline and AcCoA were determined.
- Five isoelectric forms were identified, differing from the soluble enzyme.
- Acetylcholine synthesis and release were observed from intact synaptosomes and PC 12 cells, dependent on choline availability.
Conclusions:
- A distinct membrane-bound form of choline acetyltransferase exists in rat brain synaptosomes.
- This bound enzyme contributes to acetylcholine synthesis and release.
- The presence of multiple isoelectric forms suggests complex regulation of CAT activity.