Figure 1. Quenching of intrinsic fluorescence upon binding of Cu²⁺.  A: Intrinsic tryptophan fluorescence spectra of 0.1 mg/ml sample of αA-crystallin in buffer A at indicated concentrations (in µM) of Cu²⁺ are shown. B: The extent of fluorescence quenching [(F₀-F)/F₀] of 0.1 mg/ml αA- (○) and G98RαA-crystallin (●) at 25 °C is shown as a function of Cu²⁺ concentration.  The extent of fluorescence quenching of the controls, 5 μM NATA (■), 0.1 mg/ml of thyroglobulin (△) and α-synuclein (▼) as a function of Cu²⁺ concentration are also shown.  F₀ and F are the fluorescence intensities at 337 nm in the absence and in the presence Cu²⁺. In the case of α-synuclein which lacks tryptophan residue, fluorescence intensity of tyrosine residues was measured at 300 nm. Both αA- and G98RαA-crystallin exhibit similar extent of fluorescence quenching indicating that they have similar Cu²⁺-binding properties.