title: Comparison of the substrate conformations in the active sites of papain, chymopapain, ficin and bromelain by resonance Raman spectroscopy.
abstract: The resonance Raman spectra of several enzyme-substrate intermediates of papain, chymopapain, ficin and bromelain are reported. The intermediates are dithioacyl enzymes formed during the catalyzed hydrolysis of N-acylglycine thionoester substrates. Interpretation of the resonance Raman spectra allows us to compare, for the first time, the substrate geometries in a series of functioning intermediates from different enzymes. The substrates assume essentially identical conformations for papain, chymopapain and ficin and a similar, but not identical, conformation in the active site of bromelain. Each dithioacyl enzyme population appears to be made up of a single homogeneous conformational state. This state has been characterised in earlier studies of dithioacyl papains. It is designated as conformer B and is characterized by an attractive contact between the substrate's glycinic N atom and the active site cysteine S atom. It is now apparent that conformer B is of general significance in the mechanism of cysteine proteases.
mesh_terms: D001665:Binding Sites; D001963:Bromelains / Q000378:metabolism*; D002917:Chymopapain / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D005361:Ficain / Q000378:metabolism*; D007700:Kinetics; D010206:Papain / Q000378:metabolism*; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman
chemical_list: D001963:Bromelains; D010450:Endopeptidases; D010206:Papain; D005361:Ficain; D002917:Chymopapain