Nitrogenase activity and membrane electrogenesis in the cyanobacterium Anabaena variabilis Kütz

Relationships between nitrogenase activity and individual components of the proton electrochemical potential gradient (delta microH+) in Anabaena variabilis have been investigated. The ionophore nigericin was found to collapse delta pH in favour of the membrane potential (delta psi); hyperpolarization of delta psi was correlated with an increase in nitrogenase activity. A positive relationship between nitrogenase activity and membrane potential was also observed using the ionophore valinomycin and the uncoupler carbonylcyanide m-chlorophenylhydrazone. Furthermore, using the energy transfer inhibitor N,N'-dicyclohexylcarbodiimide, nitrogenase activity appeared to be limited by the supply of reductant rather than ATP. The data suggest, for intact filaments and isolated heterocysts, that delta psi may be important in regulating nitrogenase activity in vivo.