THE CHANGE IN HYDROGEN-BOND STRENGTH ACCOMPANYING CHARGE REARRANGEMENT - IMPLICATIONS FOR ENZYMATIC CATALYSIS

Citation
So. Shan et D. Herschlag, THE CHANGE IN HYDROGEN-BOND STRENGTH ACCOMPANYING CHARGE REARRANGEMENT - IMPLICATIONS FOR ENZYMATIC CATALYSIS, Proceedings of the National Academy of Sciences of the United Statesof America, 93(25), 1996, pp. 14474-14479
Citations number
49
Categorie Soggetti
Multidisciplinary Sciences
ISSN journal
00278424
Volume
93
Issue
25
Year of publication
1996
Pages
14474 - 14479
Database
ISI
SICI code
0027-8424(1996)93:25<14474:TCIHSA>2.0.ZU;2-6
Abstract
The equilibrium for formation of the intramolecular hydrogen bond (K-H B) in a series of substituted salicylate monoanions was investigated a s a function of Delta pK(a), the difference between the pK(a) values o f the hydrogen bond donor and acceptor, in both water and dimethyl sul foxide. The dependence of log K-HB upon Delta pK(a) is linear in both solvents, but is steeper in dimethyl sulfoxide (slope = 0.73) than in water (slope = 0.05). Thus, hydrogen bond strength can undergo substan tially larger increases in nonaqueous media than aqueous solutions as the charge density on the donor or acceptor atom increases. These resu lts support a general mechanism for enzymatic catalysis, in which hydr ogen bonding to a substrate is strengthened as charge rearranges in go ing from the ground state to the transition state; the strengthening o f the hydrogen bond would be greater in a nonaqueous enzymatic active site than in water, thus providing a rate enhancement for an enzymatic reaction relative to the solution reaction. We suggest that binding e nergy of an enzyme is used to fix the substrate in the low-dielectric active site, where the strengthening of the hydrogen bond in the cours e of a reaction is increased.