= Tungstate
<Tungstate> commonly denotes the <tungsten> oxoanion $\mathrm{WO_4^{2-}}$ and <salts> containing it. The formula specifies one <tungsten> and four <oxygen> atoms with a net charge of $-2$. The Protein Data Bank chemical-component dictionary identifies its WO4 ligand as tungstate(VI), while the corresponding PubChem record gives the dianion formula.<Tungstate WO4 in the Protein Data Bank Chemical Component Dictionary>[WO4 chemical-component summary; PubChem CID24465]{ref}
Taking each <oxygen> to have <oxidation state> $-2$, charge balance gives $x+4(-2)=-2$, hence $x=+6$ for <tungsten>. Oxidation state and net ionic charge therefore answer different questions. A neutral <salt> needs two singly charged <cations> per tungstate anion, or one doubly charged <cation>. That count balances charge without requiring the ions to form a discrete isolated molecule in a crystal.
<Tungstate> also provides an experimental structural probe. In a 1995 study of <Escherichia coli fumarase C>, a competitive tungstate derivative helped locate an <active site> containing contributions from three <protein subunits>.<The multisubunit active site of fumarase C from Escherichia coli by T. M. Weaver and others>[Abstract, tungstate derivative and multisubunit active-site assignment]{ref} Binding a detectable inorganic ion can reveal where a molecular interaction occurs. It does not by itself show that the ion is the enzyme's physiological substrate or that every binding site catalyzes a reaction.
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