title: Amino acid sequence of spinach ferredoxin:thioredoxin reductase variable subunit.
abstract: Ferredoxin:thioredoxin reductase (FTR) is an iron-sulfur protein, which, in the presence of ferredoxin and thioredoxin, catalyses the light-dependent activation of several photosynthetic enzymes. Spinach FTR consists of two dissimilar polypeptide chains, A and B, present in equal amounts. Whereas subunit B seems to be responsible for the catalytic activity, subunit A has no known catalytic function. We found earlier that the N-terminus of subunit A, also called the variable subunit, shows terminal redundancy and that 2-3 of its serine residues are phosphorylated [Tsugita, A. Yano, K., Gardet-Salvi, L. & Schürmann, P. (1991) Protein Sequence Data Anal. 4, 9-13]. We now report the complete amino acid sequence of subunit A, determined by conventional protein sequencing methods. The polypeptide chain with a calculated molecular mass of 12,669 Da consists of 112 amino acids and has a calculated isoelectric point of 5.4. The analysis of the sequence supports the idea that this subunit has no catalytic function. The comparison with a known cyanobacterial FTR reveals about 58% similarity and the striking presence of a N-terminal extension in the spinach protein. This extension may be responsible for the reported size variability of this subunit.
authors.affiliation: Research Institute for Biosciences, Science University of Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Iwadate
authors.forename: K
authors.initials: K
authors.lastname: Yano
authors.forename: M
authors.initials: M
authors.lastname: Kamo
authors.forename: L
authors.initials: L
authors.lastname: Gardet-Salvi
authors.forename: P
authors.initials: P
authors.lastname: Schürmann
authors.forename: A
authors.initials: A
authors.lastname: Tsugita
mesh_terms: D000595:Amino Acid Sequence; D003488:Cyanogen Bromide / Q000378:metabolism; D007506:Iron-Sulfur Proteins; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D016339:Spectrometry, Mass, Fast Atom Bombardment; D014675:Vegetables / Q000201:enzymology*
chemical_list: D007506:Iron-Sulfur Proteins; D010088:Oxidoreductases; C021588:ferredoxin-thioredoxin reductase; D003488:Cyanogen Bromide