Enzyme assay The activities of HAO, NR and NiR were all detected in crude extract from the cells incubated at 30C and 120 rpm for 16 h. The specific activities of HAO, NR and NiR were 0.0128 0.0027, 0.0081 0.0001 and 0.0078 0.0003 U mg1 protein, respectively. DIS