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Abstract

A kinetic analysis of enzyme inactivation due to the covalent binding of chemically modified ligands is presented. Reaction schemes similar to the Michaelis-Menten scheme have been studied as well as schemes with two states of the enzyme or two binding sites. The resulting kinetic equations lead to time courses of inactivation which can be represented by two exponential functions at least in a quasi-steady state approximation. These curves are frequently encountered in inactivation experiments. Since rapid methods for model selection and parameter estimation are desirable, but not available, a technique for a preliminary analysis of the experimental data is presented. A mere glance at the time courses shows what reaction schemes are inapplicable. For each family of inactivation curves, the construction of a line of intersections is proposed. This line contains essential kinetic information and can further be utilized for a rough parameter estimation. The technique is illustrated for three sets of experimental data where Na⁺ + K⁺-ATPase and Ca²⁺-ATPase have been inactivated by ATP-analogs.