In this study the amidase kinetics of an in situ NHase/AMase cascade system was explored as a function of operational parameters such as temperature, substrate concentration and product formation. The results indicated that controlling amidase inactivation, during acrylonitrile bioconversion, makes it possible to recover the intermediate product of the two-step reaction in almost a pure form, without using purified enzyme. It has been demonstrated, in long-term experiments performed in continuous stirred UF-membrane bioreactors, that amidase is kinetically controlled by its proper substrate, depending on the structure, and by acrylonitrile. Using acrylamide, AMase-stability is temperature dependent (5 degrees C, k(d) = 0.008 h(-1); 30 degrees C k(d) = 0.023 h(-1)). Using benzamide, amidase is thermally stable up to 50 degrees C and no substrate inhibition/inactivation occurs. With acrylonitrile, AMase-activity and -stability remain unchanged at concentrations <200 mM but at 200 mM, 35 degrees C, after 70 h process, 90% irreversible inactivation occurs as no AMase-activity on benzamide revives. (C) 2013 Elsevier Ltd. All rights reserved.