Thioredoxins and the redox modulation of glucose-6-phosphate dehydrogenase in Anabaena sp. strain PCC 7120 vegetative cells and heterocysts.

Glucose-6-phosphate dehydrogenase (G6PDH) was isolated from heterocysts and vegetative cells of Anabaena sp. strain PCC 7120. Both enzyme preparations proved to be more active in their oxidized than in their reduced forms. At least one protein with thioredoxin activity was found in Anabaena sp. which, if reduced with dithiothreitol, deactivated the G6PDH preparations. The deactivated heterocyst G6PDH could be reactivated neither by O2 nor by oxidized thioredoxin. Reactivation of the enzyme was, however, achieved by oxidized glutathione or H2O2. The active form of Anabaena G6PDH was readily deactivated by heterologous thioredoxin(s). The Anabaena thioredoxin(s) modulated heterologous enzymes.