Abstract
Calcium ions are shown to have a marked pH-dependent effect on the kinetics of benzoyllarginine ethyl ester hydrolysis by porcine enteropeptidase (EC 3.4.21.9). Below pH 6.0, calcium ions stimulate benzoylarginine ethyl ester hydrolysis but inhibit this activity above pH 6.0. This effect is mainly on the K m for benzoylarginine ethyl ester. At pH 5.3, 2 mM calcium ions reduce the K m for benzoylarginine ethyl ester from 0.31 mM to 0.26 mM while at pH 6.5 the K m increases four-fold from 0.035 mM to 0.12 mM in the presence of calcium ions. Enteropeptidase activity is not inhibited by ethylenediaminetetraacetate indicating that calcium ions are a non-essential cofactor for benzoylarginine ethyl ester hydrolysis.
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