The activation of glutamine synthetase from the cyanobacterium anabaena cylindrica by thioredoxin

The present communication defines the conditions under which thioredoxin activates glutamine synthetase from Anabaena cylindrica. Effects are obtained at pH values around neutrality, and the activation is affected by Mg(2+)-Kation in the assays. The thioredoxin systems from A.cylindrica and spinach are functionally interchangeable in the activation of glutamine synthetase. The enzyme is efficiently activated by thioredoxin(m) and also by thioredoxin(f), but at much higher concentrations. Thioredoxin(m) has previously been shown to activate NADPH-dependent malate dehydrogenase and isocitrate dehydrogenase from cyanobacteria. It is speculated that thioredoxin(m) plays a role in the differentiation of vegetative cells to heterocysts. (IFU)