Direct reduction from vanadium(V) to vanadium(IV) by NADPH in the presence of EDTA A consideration of the reduction and accumulation of vanadium in the ascidian blood cells

Vanadium(V) species are reduced to vanadium(IV) directly by NADPH in the presence of EDTA. At neutral pH. vanadium(V)-EDTA complex, [VO2(EDTA)](3-) (20 mM) was almost completely reduced to [VO(EDTA)](2-) directly by NADPH (200 mM) after 15 h under aerobic and anaerobic conditions. The reduction is markedly accelerated at low pH. At pH 3, the vanadium(V) complex (20 mM) was reduced by NADPH (20 mM) within 1 h. Oxygen had little effect, but inhibited the reduction to some extent at low pH. At low pH, simple vanadium(V) species were also partly reduced without the assistance of EDTA, resulting in the formation of mixed-valence (V(IV)-V(V)) polynuclear species. The accumulation and reduction of vanadium in the vanadocytes of ascidians are discussed based on the present results. (C)1999 Elsevier Science Inc. All rights reserved.