Green Algae (Scenedesmus obliquus) Contain Three Thioredoxins of Regular Size

Petra Langlotz, Wolfgang Wagner, and Hartmut Follmann Fachbereich Chemie der Philipps-Universität, Biochemie, Hans-Meerwein-Straße. D-3550 Marburg, Bundesrepublik Deutschland Z. Naturforsch. 41c, 979—987 (1986); received August 1/September 19, 1986 Am ino Acid Composition, A lgae, Ribonucleotide Reductase, Scenedesmus obliquus, Thio­ redoxin A comprehensive thioredoxin profile of Scenedesmus obliquus has been established by chromatography of heat-stable protein extracts on five different ion exchange, gel permeation, and affinity chromatography columns and using three different assay systems including hom olo­ gous S. obliquus ribonucleotide reductase, chloroplast fructose-bis-phosphatase, and N A D P malate dehydrogenase. Four different thioredoxins were purified to homogeneity. Besides the large chloroplast thioredoxin/described previously, the algae contain three proteins of molecular weight 12,000 designated thioredoxin I, II, and III. They bind specifically to antibodies against E. coli thioredoxin. Chloroplast-free mutant algae (strain C-2A') lack thioredoxin / but contain all three regular thioredoxins. Species I and II have very similar amino acid composition and enzyme-stimulating activities. They are considered cytoplasmic thioredoxins which serve as hydrogen donors in algal deoxyribonucleotide biosynthesis. Thioredoxin III is of low activity towards all the presently tested enzymes and its physiological role remains unknown; its role as a glutaredoxin could be excluded. All non-photosynthetic plant cells analyzed so far (mutant algae, seeds, and roots) contain a set of three regular-size thioredoxins.