Tyrosine and tyrosinate fluorescence of pig intestinal Ca2+-binding protein.
The single tyrosine residue in both pig and cow intestinal Ca2+-binding proteins fluoresces at 303 nm although the crystal structure of the cow protein shows a hydrogen bond between the hydroxy group of the tyrosine and glutamate-38 [Szebenyi & Moffat (1986) J. Biol. Chem. 261, 8761-8777]. The latter interaction suggests that tyrosinate fluorescence should dominate the emission spectra of these proteins. A fluorescence difference spectrum, produced by subtracting the spectrum of free tyrosine from the spectrum of the protein, gives a peak at 334 nm due to ionized tyrosine. That this component of the emission spectrum is not due to a tryptophan-containing contaminant is shown by its elimination when the protein is denatured by guanidine and when glutamate-38 is protonated. We conclude that, in solution, the tyrosine residue in this protein interacts occasionally with glutamate-38 but that a permanent hydrogen bond is not formed.
D000818:Animals; D002135:Calcium-Binding Proteins; D019791:Guanidine; D006146:Guanidines; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007422:Intestines / Q000032:analysis*; D013050:Spectrometry, Fluorescence; D013552:Swine; D014443:Tyrosine / Q000032:analysis*
D002135:Calcium-Binding Proteins; D006146:Guanidines; D014443:Tyrosine; D019791:Guanidine