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

Abstract

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 Mg²⁺ 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.

Glutamine synthetase, thioredoxin, nitrogen assimilation, cyanobacteria, Anabaena cylindrica