Fluoroaluminates activate transducin‐GDP by mimicking the γ‐phosphate of GTP in its binding site

Fluoride activation of the cGMP cascade of vision requires the presence of aluminum, and is shown to be mediated by the binding of one AlF‐ 4 to the GDP/GTP‐binding subunit of transducin. The presence of GDP in the site is required: AlF 4 − is ineffective when the site is empty or when GDPßS is substituted for GDP. This sensitivity to the sulfur of GDPßS suggests that AlF 4 − is in contact with the GDP. Striking structural similarities between AlF 4 − and PO 4 −1 lead us to propose that AlF 4 − mimics the role of the γ‐phosphate of GTP.