A vanadium-binding protein was isolated from the culture medium of the vana
dium-reducing bacterium Pseudomonas isachenkovii by utilizing vanadate as t
he terminal electron acceptor upon anaerobic respiration. The protein was a
ssociated with vanadium at a molar ratio of similar to 1:20. It was purifie
d to homogeneity and separated into three components by treatment with 1 M
HCl followed by gel filtration: a protein, a vanadium-binding ligand, and i
norganic vanadium, Electron paramagnetic resonance analysis showed that van
adium was associated with the protein in the 4+ oxidation state, The distri
bution of vanadium within the cell was studied by electron microscopy and x
-ray microanalysis of P. isachenkovii cells. The results suggest that vanad
ium, accumulated in special swells on the surface of the cell membranes, is
reduced and excreted to the medium.