Fluorescence properties of native and chemically modified mesentericopeptidase

Studies on the fluorescence properties of native mesentericopeptidase as a function of the temperature and/or in the presence of either neutral or ionic fluorescence quenchers demonstrate that the intrinsic emission f this protein is dominated by a partially exposed tryptophyl residue, which is probably located in a site of high dielectric constant containing positively charged amino acid side chains. One largely exposed tryptophan contributes about 14% of the total emission, whereas one deeply buried tryptophan is virtually non-fluorescent. The conversion of the active site serine to cysteine and the insertion of either one phenylmethanesulfonyl or one dansyl substituent into the active site induce only subtle differences in the conformational properties with respect to the native protein; in particular, the mutual distances and orientation between the 13 tyrosyl and 3 tryptophyl residues are unaffected, as shown by singlet-singlet energy transfer experiments.