TY - JOUR
T1 - Identification of an active site arginine in rat choline acetyltransferase by alanine scanning mutagenesis
AU - Wu, D.
AU - Hersh, L. B.
PY - 1995/12/8
Y1 - 1995/12/8
N2 - Kinetic as well as chemical modification studies have implicated the presence of an active site arginine in choline acetyltransferase, whose function is to stabilize coenzyme binding by interacting with the 3'- phosphate of the coenzyme A substrate. In order to identify this residue seven conserved arginines in rat choline acetyltransferase were converted to alanine by site-directed mutagenesis, and the properties of these mutants were compared with the wild type enzyme. Substitution of arginine 452 with alanine resulted in a 7-12-fold increase in the K(m) for both CoA and acetylcholine as well as k(cat), with little change in the K(m) for dephospho-CoA. Product inhibition studies showed choline to be a competitive inhibitor with respect to acetylcholine, indicating R452A follows the same Theorell-Chance kinetic mechanism as the wild type enzyme. Similar results were obtained with R452Q and R452E, with the latter showing the largest changes in kinetic parameters. These findings are consistent with Arg-452 mutations increasing the rate constant, k5, for dissociation of the coenzyme from the enzyme. Direct evidence that arginine 452 is involved in coenzyme A binding was obtained by showing a 5-10-fold decrease in affinity of the R452A mutant for coenzyme A as determined by the ability to protect against phenylglyoxal inactivation as well as thermal inactivation.
AB - Kinetic as well as chemical modification studies have implicated the presence of an active site arginine in choline acetyltransferase, whose function is to stabilize coenzyme binding by interacting with the 3'- phosphate of the coenzyme A substrate. In order to identify this residue seven conserved arginines in rat choline acetyltransferase were converted to alanine by site-directed mutagenesis, and the properties of these mutants were compared with the wild type enzyme. Substitution of arginine 452 with alanine resulted in a 7-12-fold increase in the K(m) for both CoA and acetylcholine as well as k(cat), with little change in the K(m) for dephospho-CoA. Product inhibition studies showed choline to be a competitive inhibitor with respect to acetylcholine, indicating R452A follows the same Theorell-Chance kinetic mechanism as the wild type enzyme. Similar results were obtained with R452Q and R452E, with the latter showing the largest changes in kinetic parameters. These findings are consistent with Arg-452 mutations increasing the rate constant, k5, for dissociation of the coenzyme from the enzyme. Direct evidence that arginine 452 is involved in coenzyme A binding was obtained by showing a 5-10-fold decrease in affinity of the R452A mutant for coenzyme A as determined by the ability to protect against phenylglyoxal inactivation as well as thermal inactivation.
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U2 - 10.1074/jbc.270.49.29111
DO - 10.1074/jbc.270.49.29111
M3 - Article
C2 - 7493935
AN - SCOPUS:0028883982
SN - 0021-9258
VL - 270
SP - 29111
EP - 29116
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 49
ER -