Hemoglobin Fluorescence

Protein structural analysis took a big leap forward with the discovery of aromatic amino acid and protein fluorescence (1 –4 ). The intrinsic fluorescence of proteins is a highly sensitive reporter of conformational change at or near the fluorescent tryptophans (Trp) and tyrosines (Tyr). Phenylalanine also exhibits ultraviolet (UV) fluorescence excitation and emission, with a low quantum yield that becomes insignificant in proteins containing Tyr and Trp. The binding of specific extrinsic fluorescent probes allows the site-specific probing of other microdomains or nonfluorescent side chains. Fluorescence resonance energy transfer measurements serve as a “spectroscopic ruler” to measure intramolecular and intermolecular distances and may also be used to ascertain the magnitude of conformational change on ligand binding, protein folding, and protein-protein interactions ([5 ]; for basic principles of fluorescence, see ref. 6 ).