Practice question

Hemocyanin, respiratory copper protein of arthropods and molluscs, binds oxygen via binuclear copper centers rather than iron heme. Deoxygenated Cu(I) form is essentially colorless with weak absorption, whereas oxy-hemocyanin with Cu(II)-peroxide complex exhibits intense ligand-to-metal charge transfer bands near 340 nm and 580 nm conferring characteristic blue color. These electronic transitions are quantifiable by UV-Visible absorption spectroscopy using Beer-Lambert law. Changes in band intensity and position report oxidation state, oxygen saturation and allosteric regulation. Fluorescence lacks suitable chromophore, mass spectrometry cannot monitor reversible oxygenation dynamically in solution.