Enzyme-loaded polymeric vesicles, or polymersomes, can be regarded as nanoreactors, which, for example, can be applied as artificial organelles. We implemented a naturally occurring enzymatic cascade reaction in two types of polymersomes, which are known to possess different permeability properties. The selected cascade reaction involved the antioxidant enzymes superoxide dismutase (SOD1) and catalase (CAT) for combating oxidative stress. The activities of both enzymes were investigated by spectrophotometric and electrochemical assays. Whereas the SOD1 substrate (the radical anion superoxide, O-2(center dot-)) was able to penetrate both membranes equally well, the CAT substrate (H2O2) showed different rates of diffusion. When O-2(center dot-) was generated inside polymersomes filled with both SOD1 and CAT, the activities of the two systems were comparable again.