title: Fluorescence studies with potato carboxypeptidase inhibitor.
abstract: Potato carboxypeptidase inhibitor (CPI) is a 39-residue globular protein whose X-ray structure is known. The protein's two tryptophan residues (W22 and W28) appear to be on the surface in the crystal structure. The fluorescence spectrum of CPI has a maximum at 344 nm. Acrylamide solute quenching yields an upward curving Stern-Volmer plot with KSV approximately 9 M-1. KI quenching yields a linear plot with KSV approximately 5.5 M-1. These studies indicate that emission occurs from a solvent exposed residue(s). Fluorescence lifetime measurements were fitted to a biexponential decay law with tau 1 = 0.9 ns. f1 = 0.22 and tau 2 = 3.9 ns. Anisotropy decay data were described by a single rotational correlation time of 1.2 ns. This value is somewhat small for the global rotation of a protein of this size. The low temperature phosphorescence of CPI shows a biexponential decay, with a rapidly decaying 0.5-1.0 second component. The triplet state of at least one of the two tryptophan residues must be perturbed by interaction with nearby disulfide bonds.
authors: Department of Biochemistry, University of Missouri, Columbia.
authors: C A
authors: CA
authors: Ghiron
authors: M R
authors: MR
authors: Eftink
authors: J
authors: J
authors: Longworth
authors: C
authors: C
authors: Ryan
mesh_terms: D000178:Acrylamides; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors*; D010940:Plant Proteins / Q000737:chemistry*; D011480:Protease Inhibitors; D011198:Solanum tuberosum / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000178:Acrylamides; D010940:Plant Proteins; D011480:Protease Inhibitors; D002268:Carboxypeptidases