Redox control of hydrogenase activity in the green alga Scenedesmus obliquus by thioredoxin and other thiols

The activity of the NiFe-hydrogenase from the green alga Scenedesmus obliqu us is inhibited by both algal thioredoxins f and I+II, and by Escherichia c oli thioredoxin, The strongest inhibition was observed with homologous chlo roplastic thioredoxin f (I-50 = 21 nM) and E. coli thioredoxin (I-50 = 83 n M). For the homologous cytoplasmic thioredoxins I+II an I-50 of 667 nM was determined. Glutathione shows a similar but much less pronounced inhibitory effect whereas dithiothreitol had no effect. In addition to glucose-6-phos phate dehydrogenase, NiFe-hydrogenase is only the second enzyme known to be inhibited by reduced thioredoxin. (C) 1999 Federation of European Biochemi cal Societies.