Contribution of individual tryptophan residues to the fluorescence spectrum of native and denatured forms of humans carbonic anhydrase II

Two-dimensional NMR spectroscopic studies of the wild-type human carbonic anhydrase II and its mutants, resulting from the replacement of tryptophan residues by cysteine or phenylalanine, reveal no significant changes in protein structure. The two tryptophan residues, Trp 97 and Trp 245, contribute 52% and 38%, respectively, to the fluorescence spectrum. His64 quenches the fluorescence from Trp5, while there is a transfer of energy from Trp192 to Trp209 and from Trp16 to Trp5. The beta-strands 3-7 of the native protein correspond to the core of a globule intermediate, as revealed by a study of the tryptophan environment through acrylamide quenching of the fluorescence.