A general expression for coupled enzyme assays of hysteretic enzymes.

A general description of a system consisting of a hysteretic enzyme and a series of coupling enzymes is presented. The chloroplast enzyme sedoheptulose-1,7-bisphosphatase and a sequence of three coupling enzymes is used as an example. An analysis using first-order rate equations for the coupling enzymes shows that the observed relaxation time of the system is the sum of the relaxation times of the coupling enzymes and that of the hysteretic enzyme. The behaviour of a system with relatively low concentrations of coupling enzymes, where the first-order assumption is not valid, is analysed by computer stimulation. Several methods for the accurate determination of the relaxation time of the hysteretic enzyme are discussed.