title: The catalytic mode of cysteine proteinases of papain (C1) family.
abstract: The Proton Inventory (PI) method has been applied in the hydrolysis of synthetic substrates by papain, chymopapain and stem bromelain, comparing also their corresponding pH-(k(cat)/K(m)) profiles, and it was found: (a) k(cat)/K(m)=k(1), and thus K(S)=k(2)/k(1) is a dynamic equilibrium constant, (b) bowed-downward PI for k(cat)/K(m) exhibiting large inverse SIE, and (c) linear PI exhibiting large normal SIE for K(S), k(2) and k(3). A novel finding of this work is that the association of substrates onto all three studied cysteine proteinases proceeds via a stepwise pathway, in contrast to purely concerted pathways found previously for both acylation and deacylation. A hydrogen bond, which seems more likely to be developed across a pK(a)-value close to 4.00, connecting [see text] (papain/chymopapain or bromelain numbering), constitutes another novelty of this work.
authors.affiliation: University of Ioannina, Department of Chemistry, Laboratory of Biochemistry, 451-10 Ioannina, Greece.
authors.forename: Leonidas G
authors.initials: LG
authors.lastname: Theodorou
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Bieth
authors.forename: Emmanuel M
authors.initials: EM
authors.lastname: Papamichael
mesh_terms: D001963:Bromelains / Q000737:chemistry; D002384:Catalysis; D002917:Chymopapain / Q000737:chemistry; D003903:Deuterium / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010206:Papain / Q000737:chemistry*; D011522:Protons
chemical_list: D011522:Protons; D001963:Bromelains; D003903:Deuterium; D010206:Papain; D002917:Chymopapain