Recent perspectives into biochemistry of decavanadate

Figure 1 Schematic structure of V₁₀ (V₁₀O₂₈^6-). Va, Vb and Vc represent the three different types of vanadium atoms described in the text.

Figure 2 Modes of calcium translocation by SR calcium pump as affected by different vanadate oligomers. V₁: Monomeric vanadate; V₄: Tetrameric vanadate; V₁₀: Decameric vanadate. Only V₁₀, and not V₁, was shown to inhibit calcium uptake in conditions 1 and 3, that is, when ATPase activity is coupled to calcium transport. V₁ only inhibits the ATPase in condition 2, where the calcium gradient is destroyed by oxalate or phosphate.

Figure 3 Relevant steps of ATP hydrolysis by actomyosin complex. The dominant process of ATP hydrolysis observed in vitro is indicated by the filled arrows. M: Myosin; Vi: Orthovanadate; V₁₀: Decavanadate. V₁₀, can blocked the process at two steps, without or with F-actin: before ATP hydrolysis and before product release, just before power stroke.

Figure 4 F-actin cysteine redox state, after 20 min exposure to decavanadate. Titration of cysteine was performed with 0.1 mmol/L 5,5’-ditiobis-(2-nitrobenzoic acid) and 2 μmol/L actin in 2 mmol/L Tris (pH 7.5), and 0.2 mmol/L CaCl₂. The increase in absorbance at 412 nm was continuously recorded over 10 min; To measure total cysteines the samples were treated afterwards with 1% SDS, and the absorbance was measured, over 15-30 min, until a steady value was reached. Titration with decavanadate produced a dose-dependent decrease in F-actin total cysteines, while Cys-374 (also named "fast cysteine") is reduced. The results shown are the average of triplicate experiments.

Figure 5 Exchange of bound ε-ATP of G-actin with ATP. Actin monomers (5 μmol/L) were incubated for 20 min with 0-200 μmol/L decavanadate, in 2 mmol/L Tris-HCl (pH 7.5), 0.2 mmol/L CaCl₂. The nucleotide exchange was monitored by the fluorescence decrease (λex = 350 nm; λem = 410 nm), as ε-ATP was replaced by ATP. Data are plotted as mean ± SD. The results shown are the average of triplicate experiments.

Figure 6 Scheme of proposed decavanadate (V₁₀) cellular targets. V₁₀ uptake through anionic channels (AC). Decavanadate might interact with membrane proteins. V₁₀ formation upon intracellular vanadium acidification in cytosol, but most probably in acidic organelles. Reduction of monomeric vanadate (V₁) by antioxidant agents. Binding of V₁₀ to target proteins; it is proposed that V₁₀ accumulates in subcellular organelles, such as mitochondria, affecting its function. Decavanadate also targets the contractile system, and its regulation, as well as calcium homeostasis (adapted from[14]).