Mn2+ transport in the unicellular cyanobacterium Anacystis nidulans

Mn²⁺ uptake by wild type of Anacystis nidulans IU 625 follows Michaelis-Menten type kinetics with apparent saturation at 27 μmol/l of Mn²⁺. Lineweaver-Burk plot of the data reveals a Km of 25 μmol/l and V_max of 1.2 nmol/mg protein · min. The uptake values at different pH (pH 4.0 to 9.0) exhibit a characteristic profile with an optimum at pH 6.0. The Mn²⁺ uptake rate in the dark is found to be similar to that in the light suggesting that energy for transport may not be directly derived from light reactions. The system seems to be specific for Mn²⁺ transport since simultaneous addition of Mg²⁺ partially inhibited the uptake in a competitive manner. Further, the alterations in Km and V_max values of mutants with respect to that of wild type strains suggest a genetic control of the transport system.