Carbon-13 NMR study of the ionizations within a trypsin-chloromethyl ketone inhibitor complex
- 1 July 1985
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 24 (14) , 3478-3487
- https://doi.org/10.1021/bi00335a014
Abstract
13C NMR is used to detect ionizations within a trypsin-chloromethyl ketone inhibitor complex. The pKa values observed are compared with those predicted by free-energy relationships. For the denatured/autolyzed inhibitor complex, a pKa = 5.26, is observed, which is assigned to the ionization of the imidazole of histamine-57. For the intact inhibitor complex a pKa = 7.88 is determined. This pKa is assigned to the ionization of the hemiketal hydroxyl (pKa = 7.88-8.1) and provides the first direct evidence that the serine proteases are able to stabilize the oxyanion of tetrahedral adducts. Indirect evidence is adduced that the imidazole pK1 of histidine-57 is .gtoreq. 8.1. There may be extra fast exchange line broadening, which could result from rapid tautomeric exchange between neutral and zwitterionic species within the inhibitor complex. The significance of these results from the catalytic mechanism of serine proteases is discussed.This publication has 11 references indexed in Scilit:
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