[Ferredoxin from Bumilleriopsis filiformis Vischer]

Ferredoxin from the alga Bumilleriopsis filiformis Vischer (Xanthophyceae) is characterized by comparing some of its properties with spinach ferredoxin.It is similar to the known plant ferredoxins in the following points: a) Absorption spectrum. b) Molecular weight. c) Amino acid composition (approx. 100 amino acid residues). d) Uptake of 1 electron upon complete reduction and a 50 per cent decrease of the optical density at 420 nm. e) 2 non-heme iron atoms per molecule, which do not exchange with an iron isotope. f) SH-groups of the native protein do not react with DTNB. Bumilleriopsis ferredoxin differs from known plant ferredoxins in the following points: a) Greater stability towards atmospheric oxygen when gently heated. b) Only 1 detectable acid-labile sulfur atom per molecule. c) Dialysis against EDTA: by this procedure a part of the iron but none of the acid-labile sulfur is removed. With spinach ferredoxin a part of both elements is removed simultaneously. d) Greater reactivity with ferredoxin-NADP reductase from Bumilleriopsis than with that from spinach. With spinach ferredoxin no substantial difference between the reaction rates of the two reductases is observed (see Böger, 1969 b). The results may indicate an active center in Bumilleriopsis ferredoxin consisting of 1 atom iron and 1 atom acid-labile sulfur.