Abstract
The Raman spectra of Bence‐Jones proteins (BJP) were measured for their native and denatured states. All of the native BJPs investigated gave amide I at 1670–1675 cm^−1^ and amide III at 1242–1246 cm^−1^. Although the amide I was shifted to 1667 cm^−1^ upon the LiBr, acid, and thermal denaturation, as expected, the amide III frequency was unaltered, indicating that the antiparallel β‐ and disordered structures of BJP provide amide III at almost the same frequencies. The intensity of the 880‐cm^−1^ line of native BJP was relatively intense compared with that of amino acid mixed solution in which the mole ratios of Trp, Phe, and Tyr were adjusted to reproduce the corresponding ratios of BJP. However, the intensity was evidently reduced upon LiBr, acid, and thermal denaturation, approaching that of the amino acid mixture. Thus, the intensity of the 880‐cm^−1^ line is proposed as a practical probe for the environment of Trp residues. The pH dependence of the intensity of the 880‐cm^−1^ line suggests that one of two buried Trp residues is exposed between pH 4 and 3.2 and the other between pH 3.2 and 1.4. The variable fragment (V~L~) of BJP (Tod) exhibited a SS stretching Raman line at 525 cm^−1^. Provided that the crystallographic data of the V~L~ of BJP is applicable to V~L~ of BJP (Tod), the 525 cm^−1^ of the SS stretching frequency should be assigned to a TGG conformation of linkage, but not to the AGT or AGG conformation. This supports Sugeta's model rather than Scheraga's model.