The catalytic mode of cysteine proteinases of papain (C1) family |
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Authors: | Theodorou Leonidas G Bieth Joseph G Papamichael Emmanuel M |
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Institution: | University of Ioannina, Department of Chemistry, Laboratory of Biochemistry, 451-10 Ioannina, Greece. |
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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. |
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