2.7.2.1. Nitrate reductase (NR; EC 1.6.6.1) and nitrite reductase (NiR; EC 1.7.7.1) activities
The activities of Nitrate reductase (NR; EC 1.6.6.1) and nitrite reductase (NiR; EC 1.7.7.1) were performed with dithionite-reduced methyl viologen as reductant in cyanobacterial cells made permeable by alkyltrimethy­lammonium bromide (MTA) in the reaction mixture following the method of Herrero et al. (1981, 1984) and Herrero and Guerrero (1986), respectively. The NO2 ions in cell free media were estimated according to Snell and Snell (1949). One unit (U) NR activity is defined as 1 nmol NO2 for­med min–1. One unit (U) NiR activity is defined as 1 nmol NO2 consumed min–1.