Effects of Calcium Ion on the Catalytic Activity of α-Chymotrypsin in Organic Solvents

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Addition of small amounts of calcium ion markedly accelerated the transesterification of N-acetyl-L-tyrosine methyl ester to its ethyl ester by the catalysis of α-chymotrypsin in organic solvents. Maximum increase of the reaction rate was about 12-fold in the presence of 25 μM of calcium ion in ethanol. The rate increase was strongly dependent on calcium ion concentration and nature of organic solvents. Esterification of N-acetyl-L-tyrosine and hydrolysis of N-acetyl-L-tyrosine ethyl ester by α-chymotrypsin in organic solvents were also accelerated by calcium ion. The reactions obeyed Michaelis-Menten kinetics, and the acceleration of the reactions was due to the increase in k_cat.