Entropic and enthalpic components of catalysis in the mutase and lyase activities of Pseudomonas aeruginosa PchB
Meneely, Kathleen M.
Lamb, Audrey L.
American Chemical Society
Scholarly/refereed, publisher version
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The isochorismate-pyruvate lyase from Pseudomonas aeruginosa (PchB) catalyzes two pericyclic reactions, demonstrating the eponymous activity and also chorismate mutase activity. The thermodynamic parameters for these enzyme-catalyzed activities, as well as the uncatalyzed isochorismate decomposition, are reported from temperature dependence of kcat and kuncat data. The entropic effects do not contribute to enzyme catalysis as expected from previously reported chorismate mutase data. Indeed, an entropic penalty for the enzyme-catalyzed mutase reaction (ΔS‡ = -12.1 ± 0.6 cal/molK) is comparable to that of the previously reported uncatalyzed reaction, whereas that of the enzyme-catalyzed lyase reaction (ΔS‡ = -24.3 ± 0.6 cal/molK) is larger than that of the uncatalyzed lyase reaction (-15.77 ± 0.02 cal/molK) documented here. With the assumption that chemistry is rate-limiting, we propose that a reactive substrate conformation is formed upon loop closure of the active site and that ordering of the loop contributes to the entropic penalty for converting the enzyme substrate complex to the transition state.
This document is the Accepted Manuscript version of a Published Work that appeared in final form in the Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/ja202091a.
Luo, Q., Meneely, K. M., & Lamb, A. L. (2011). Entropic and enthalpic components of catalysis in the mutase and lyase activities of Pseudomonas aeruginosa PchB. Journal of the American Chemical Society, 133(18), 7229–7233. http://doi.org/10.1021/ja202091a
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