ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Several physical and kinetic properties of highly purified choline acetyltransferase (EC 2.3.1.6., Acetyl-CoA:choline O-acetyltransferase) from rat and bovine brain were investigated. The molecular weight of the enzyme from rat cerebrum was 65,000 measured by gel filtration and 66,000 measured by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Two species of the enzyme detected in bovine caudate nuclei were studied using the same procedures. The major transferase species, bovine I (Bov I), yielded values of molecular weights of 69,000 and 70,000, respectively. The minor bovine acetylase species (Bov II) had a molecular weight of 67,000 daltons by gel filtration. The dependence of reaction rates catalyzed by Bov I and rat choline acetyltransferase on temperature and pH was examined. The two enzymes possess apparent activation energies of 21.0 and 20.0 kcal/mol, respectively. Both displayed a rather broad pH optimum, extending into the alkaline region, and were activated by either NaCl or KCl. Neither enzyme was activated or inhibited by a wide range of concentrations of acetyl-CoA or choline. Initial velocity studies for both enzymes indicated a sequential mechanism, in which both substrates must bind before either product is released. For Bov I, the Michaelis constants for acetyl-CoA and choline were 16.5 μM and 0.714 mm, respectively; the equivalent constants for rat CAT were 46.5 μM and 1.0 mm. Product inhibition studies with the rat enzyme showed that acetylcholine was competitive with respect to choline, and noncompetitive with respect to acetyl-CoA, while CoA inhibited competitively with respect to acetyl-CoA and noncompetitively with respect to choline. The values of K1, obtained for acetylcholine and CoA were 45.5 mm and 37.7 μM, respectively.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1980.tb06609.x
Permalink