Abstract A mathematical model applicable to the analysis and simulation of a heterogeneous bienzymatic reaction system is presented. The glucose oxidase–catalase (GOD–CAT) system co-encapsulated within hydrogel-membrane liquid-core capsules was chosen as the model system in this study. The proposed model considers a non-uniform biocatalyst concentration profile within the support and the deactivation phenomena of the two enzymes. Simulation experiments allowed us to elucidate the distribution of the two enzymes within the capsules. It seemed that GOD was distributed across the whole of the particle while CAT was confined almost exclusively to the core of the capsule. From the simulated glucose and hydrogen peroxide concentrations within the capsules, it was deduced that the hydrogen peroxide formed in the glucose oxidation reaction led firstly to the deactivation of the catalase and, after this point, GOD deactivation was accelerated.