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.