Comparative study on the active sites of ficin and papain by the spin labeling method.
Ficin was alkylated with a series of haloacetamide spin labels with various distances between the spin probes and reactive groups. From the relation of these distances to the tau c values of the labels incorporated into protein, it was estimated that the depth of the active site hole of ficin is ca. 8 A. The results are somewhat different from those reported previously for papain (S. Nakayama et al. (1981) Biochem. Biophys. Res. Commun. 98, 471-475). Examination of the pH dependence of the ESR spectra for ficin and papain alkylated with an iodoacetamide or a maleimide spin label suggested that these enzymes have an amino acid residue of pKa 4 (probably a histidine residue) around the active site cysteine and that the active site conformations change at around pH 5.
Nakayama
S
S
University of Library and Information Science, Ibaraki.
Watanabe
T
T
Takahashi
K
K
Hoshino
M
M
Yoshida
M
M
D001665:Binding Sites; D003546:Cysteine Endopeptidases / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy; D005361:Ficain / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D010206:Papain / Q000032:analysis*; D011487:Protein Conformation; D013113:Spin Labels
D013113:Spin Labels; D003546:Cysteine Endopeptidases; D010206:Papain; D005361:Ficain