Exposure of Pseudomonas stutzeri to NO3- starvation resulted in inactivation of the second dissimilatory reductase, i.e. NO2- reductase, of the denitrification process. Inactivation of this enzyme was dependent on the duration of the exposure, which subsequently gave rise to variable (0-100%) extent of NO2- accumulation after NO3- re-supply. The present study explains and simulates this phenomenon. An over-flow model was investigated, which included not only conventional enzymatic kinetics but also the dynamic enzyme amount with respect to degradation and resynthesis. The output of the model had a generally good fit to the actual experimental results. Hence, this model reveals a basic mechanism which explains the variable degree of NO2- accumulation by a single species under conditions of alternating NO3- availability.