The structure of sickle cell hemoglobin (Hb S) (beta6 Glu --> Val) fibers was probed using UV resonance Raman (UVRR) spectroscopy. For these studies a functional analogue of Hb S, fluoromet Hb S, was used to study structural changes that accompany fiber formation. The amide backbone and aromatic residues of Hb S were selectively investigated using excitation wavelengths of 210, 215, and 230 nm. In the 210 and 215 nm excited fiber spectra, the intensity of all Phe bands increases dramatically. At the excitation wavelengths used, the Phe signal intensity reflects the local environment and increases linearly with increasing ethylene glycol concentration. Thus, UVRR fiber spectra are suggestive of an increase in hydrophobicity of the Phe local environment, which results from the formation of lateral and axial fiber contacts that are primarily nonpolar and hydrophobic in nature. The observed UVRR signal is assigned to the beta (1)85 Phe residue, which, together with the beta (1)88 Leu residue, forms a hydrophobic lateral contact with the mutated beta (2)6 residue. In addition, 230 nm difference spectra are suggestive that H-bonds stabilizing the alpha (1)beta (2) interface are stronger in fibers than in unassociated T-state tetramers. The W3 mode in fiber difference spectra occurs at 1550 and 1565 cm(-1) indicative of an increase in Trp spectral heterogeneity. The +6 cm(-1) upshift of the W3 mode is attributed to increased hydrophobicity of Trp local environment and is assigned to the beta (2)15 Trp residue. Other structural changes include an increase in disorder upon Fiber formation, as shown by the frequencies of protein backbone amide vibrational modes. UVRR spectroscopic results are consistent with the structural details of the Hb S double strand observed crystallographically and provide new information regarding local environment and strength of H-bond interactions.