A spectroscopic investigation of S-trifluoroethylthiopapain. An investigation of the active site of papain.
The pH dependence of the 19F chemical shift and the fluorescence spectrum of S-2,2,2-trifluoro-1,1-dideuteroethyl-thio-paapain are analysed in terms of dependence on the ionisation of aspartic-acid-158 and histidine-159. The 19F probe causes negative cooperativity between these groups, and does not detected any ionisation at high pH. The intermediate chemical exchange rates for the ionisation of aspartic-acid-158 and histidine-159 allow the approxmate rate constants for proton transfer to be calculated. The rather low rate constants are explained in terms of the hydrophobicity of the active-site region and the net positive charge on the enzyme resulting from its high isoelectric point.
D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D005461:Fluorine; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007477:Ions; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010206:Papain; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis
D007477:Ions; D013438:Sulfhydryl Compounds; D005461:Fluorine; D010206:Papain