Purification and characterization of thioredoxin from the N2-fixing cyanobacterium Anabaena cylindrica

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Abstract
Thioredoxin was purified to homogeneity from the cyanobacterium A. cylindrica. The protein consists of a single polypeptide chain with a relative molecular mass of about 11,680 which has 2 cysteine residues (residues 31 and 34) in the sequence-Cys-Gly-Pro-Cys- and an isoelectric point at pH 4.55. The N-terminal amino acid sequence of 39 residues shows distinct homologies with the sequences of Escherichia coli and Corynebacterium nephridii thioredoxins. Anti-(A. cylindrica thioredoxin) antiserum was used to quantify the thioredoxin which constituted about 0.22% of the soluble protein in cell-free extracts of N2-fixing, NO3--grown or NH4+-grown A. cylindrica. Activation of fructose-1,6-bisphosphatase of A. cylindrica, activation of glutamine synthetase and NADP+-dependent malate dehydrogenase of the green alga Scenedesmus obliquus but not of A. cylindrica, and deactivation of glucose-6-phosphate dehydrogenase of the cyanobacterium A. variabilis were all achieved using the same thioredoxin species. No other thioredoxin species were detected in extracts of A. cylindrica when examined for the activation of these enzymes.
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