The behavior of remaining enzyme activity in a suicidal enzyme system

We derived an equation which describes the plot of the remaining enzyme activity versus ratio of initial concentration of suicide substrate to that of enzyme to obtain a partition ratio from the time-course of remaining enzyme activity. The simulation data calculated from the representative kinetic model for a suicide substrate were used to verify this equation, which approximated steady state kinetics. Although the time-dependent loss of enzyme activity is usually characterized by pseudo-first-order kinetics, the present results show that pseudo-first-order kinetics are followed only when the ratio of initial concentration of suicide substrate to that of enzyme is greater than the partition ratio. Our results also show that the present method can be used to obtain the partition ratio of a suicide substrate from the time-course of the remaining enzyme activity when the suicide substrate is given an arbitrary concentration of one, where the ratio of initial concentration of suicide substrate to that of enzyme is less than the partition ratio. The theoretically verified equation was also checked against reported experimental data for a microsomal enzyme system.