Theodorou Leonidas G, Bieth Joseph G, Papamichael Emmanuel M
University of Ioannina, Department of Chemistry, Laboratory of Biochemistry, 451-10 Ioannina, Greece.
Bioresour Technol. 2007 Jul;98(10):1931-9. doi: 10.1016/j.biortech.2006.07.037. Epub 2006 Sep 25.
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.
