文摘
Human placental ribonuclease inhibitor (hRI) containing six tryptophan (Trp) residues located at positions19, 261, 263, 318, 375, and 438 and its complex with RNase A have been studied using steady-state andtime-resolved fluorescence (298 K) as well as low-temperature phosphorescence (77 K). Two Trp residues inwild-type hRI and also in the protein-protein complex with RNase A are resolved optically. The accessiblesurface area values of Trp residues in the wild-type hRI and its complex and consideration of inter-Trp energytransfer in the wild-type hRI reveal that one of the Trp residues is Trp19, which is located in a hydrophobicburied region. The other Trp residue is tentatively assigned as Trp375 based on experimental results on wild-type hRI and its complex. This residue in the wild-type hRI is more or less solvent exposed. Both the Trpresidues are perturbed slightly on complex formation. Trp19 moves slightly toward a more hydrophobic region,and the environment of Trp375 becomes less solvent exposed. The complex formation also results in a moreheterogeneous environment for both the optically resolved Trp residues.
