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Kinetic and inactivation studies of recombinant Drosophila choline acetyltransferase
L Carbini1, G Rodriguez, L B Hersh
1Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235.
Abstract:
A cDNA for Drosophila choline acetyltransferase (ChAT) was expressed in E. coli and the recombinant enzyme partially purified. Kinetic analysis yielded the following constants for the recombinant enzyme; KmAcCoA = 29 microM, KmCoA = 25 microM, Kmcholine = 330 microM, and Kmacetylcholine = 2 mM. The recombinant Drosophila enzyme, like the enzyme from other species, exhibited an increase in activity as a function of increased salt concentration. Chemical modification studies using dithio-bis-nitro-2-carboxylate, butanedione, and diethylpyrocarbonate showed that the recombinant enzyme contains active site cysteine, arginine, and histidine residues. These studies demonstrate that the recombinant Drosophila ChAT possesses the same catalytic properties as the enzyme from a variety of other sources.