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Active Site of α -chymotrypsin Activation by Association-Desolvation
Saul G. Cohen, Vishnu M. Vaidya and Richard M. Schultz
Proceedings of the National Academy of Sciences of the United States of America
Vol. 66, No. 2 (Jun. 15, 1970), pp. 249-256
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/60046
Page Count: 8
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High reactivity toward α -chymotrypsin is observed for derivatives of β -arylpropionic acids of varied structure-L-α -acylamido compounds, D-cyclized compounds, and, now, L-glycolamide esters. Compensating enthalpy and entropy effects are observed which appear to be caused by changes in water of solvation. High reactivity with varied structure, and physical evidence, appear to rule out induced fit and distortion as important for this enzyme. The high reactivity results from precise fit of the hydrolyzing group at the critical serine-imidazole junction, resulting from binding of the aryl group and restriction of rotation. Part of the energy of binding is used to desolvate the reactant groups of substrate and enzyme, decreasing activation energies by several kilocalories and raising reactivity by 103 or more. Solvation by water stabilizes many compounds, allowing them to be present in solution in biological systems. Their reactions may occur as their reactivity is increased when they are desolvated and brought from solution into association with reactive groups in enzymes, membranes, and structured particles.
Proceedings of the National Academy of Sciences of the United States of America © 1970 National Academy of Sciences