title: Evidence by chemical modification that tryptophan-104 of the cysteine-proteinase inhibitor chicken cystatin is located in or near the proteinase-binding site.
abstract: The single tryptophan residue Trp-104 of chicken cystatin was modified with a 2-hydroxy-5-nitrobenzyl group. The change of the absorption spectrum of this group on binding of the modified cystatin to papain indicated a decreased environmental polarity of the probe. The modified inhibitor had about a 10(5)-fold lower affinity for papain than had intact cystatin, this being due to a higher dissociation rate constant. These results show that Trp-104 of cystatin is located in or near the proteinase-binding site of the inhibitor, in agreement with a model proposed from computer docking Experiments.
authors.affiliation: Department of Veterinary Medical Chemistry, Swedish University of Agricultural Sciences, Uppsala Biomedical Center, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Nycander
authors.forename: I
authors.initials: I
authors.lastname: Björk
mesh_terms: D000818:Animals; D001665:Binding Sites; D002645:Chickens; D015891:Cystatins / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D010206:Papain / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013452:Sulfonium Compounds; D014364:Tryptophan
chemical_list: D015891:Cystatins; D013452:Sulfonium Compounds; C024586:dimethyl(2-hydroxy-5-nitrobenzyl)sulfonium; D014364:Tryptophan; D010206:Papain