Nitrite Transport in the Unicellular Cyanobacterium Anacystis nidulans

Abstract

Summary Nitrite uptake in A. Nidulans is found to be concentration dependent and follows Michaelis-Menten type kinetics with apparent saturation at 60µM of NO2-. Lineweaver-Burk plot of the data reveals a Km of 12µM and Vmax of 2.48 nmol/mg protein - min. The uptakes conducted at different pH (pH 6.0-9.0) exhibit optimum uptake at pH 6.4. Further, a reduction in uptake rate by coldshock treated cells indicates an involvement of NO2- binding proteins. Inhibition of transport process under both the dark condition or in presence of DCMU indicates that the NO2- transport is a light dependent phenomenon. Addition of a protonophore FCCP strongly inhibits the NO2- uptake, suggesting an involvement of proton gradient in the transport process. A genetic control on the transport system is concluded on the ground that the NO2- transport is repressed in NO2- or NH4+ grown cells but not in the NO3 grown cells. In addition to this, it has also been observed that mutants differ among themselves as well as from the wild type in terms of Km and Vmax values.