Abstract
The stabilities of conalbumin and transition metal‐conalbumin complexes toward denaturants were studied by UV absorption and emission spectroscopy. The difference spectra of conalbumin and metal‐conalbumins in buffer, pH 8.0 vs. the same species in buffered 8 M urea were similar in shape with maxima at 286‐ and 292‐mμ and a negative absorption near 260‐mμ. The Δε~292~ for colored Fe‐, Cr‐, Cu‐, and Mn‐conalbumins was 5 × 10^3^ less than that for conalbumin and colorless Co‐, Zn‐, Cd‐, Ni‐, and Mn‐conalbumins, indicating that two tryptophanyl residues were bound to or protected by metal ions in the former but not the latter cases. The F~350~ of conalbumin was quenched up to 65% on formation of the colored complexes, but not on formation of colorless complexes. The F~350~ of conalbumin was strongly quenched by increasing temperature (0 to 70°) or pH (5 to 12.5), whereas that of Fe^+3^‐conalbumin was essentially independent of these variables. These results indicate the presence of tryptophanyl residues, in addition to the known tyrosyl and histidyl residues, in conalbumin‐metal binding sites, and suggest that charge‐transfer interactions between these tryptophanyl residues and the bound metals is probably responsible, at least in part, for color formation, as well as for the marked increase in stability of these colored complexes.