Theoretical and Experimental Analysis of Ionization Equilibria in Ovomucoid Third Domain
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- 作者：William R. Forsyth ; Michael K. Gilson ; Jan Antosiewicz ; Olav R. Jaren ; and Andrew D. Robertson
- 刊名：Biochemistry
- 出版年：1998
- 出版时间：June 16, 1998
- 年：1998
- 卷：37
- 期：24
- 页码：8643 - 8652
- 全文大小：199K
- 年卷期：v.37,no.24(June 16, 1998)
- ISSN：1520-4995
文摘
2D-NMR experiments were used to determine thepKa values ranging from 8.0 to 
11.1ofseven basic residues in turkey ovomucoid third domain (OMTKY3) and werecompared to values predictedas described by Antosiewicz et al. [(1996) Biochemistry 35,7819-7833]. Lys 13, 29, and 34 werepreviously attributed with increasing the acidity of numerous acidicresidues [Schaller, W., and Robertson,A. D. (1995) Biochemistry 34, 4714-4723].These interactions were expected to raise thepKa values ofthose basic groups; however, the pKa values ofLys 13 and 34 are less than the model compound values.The pKa values of the other basic residuesare greater than the model compound values and, unlike theacidic residues, all are surprisingly insensitive to salt. Whilethe calculations properly predict the directionof most of the pKa shifts and provide valuableinsight into the possible molecular origins of theinteractionsthat perturb pKa values, there is a tendency tooverestimate the magnitude of the shifts and their saltdependence. Interestingly, the shapes of both the calculated andobserved transitions are often morecomplex than expected for a simple titration, suggesting thatpKa values at many sites are changingduringthe transition. Differences between predicted and experimentalpKa values and titration profiles forsomeresidues may be due to as yet uncharacterized structural changes at theextremes of pH.
11.1ofseven basic residues in turkey ovomucoid third domain (OMTKY3) and werecompared to values predictedas described by Antosiewicz et al. [(1996) Biochemistry 35,7819-7833]. Lys 13, 29, and 34 werepreviously attributed with increasing the acidity of numerous acidicresidues [Schaller, W., and Robertson,A. D. (1995) Biochemistry 34, 4714-4723].These interactions were expected to raise thepKa values ofthose basic groups; however, the pKa values ofLys 13 and 34 are less than the model compound values.The pKa values of the other basic residuesare greater than the model compound values and, unlike theacidic residues, all are surprisingly insensitive to salt. Whilethe calculations properly predict the directionof most of the pKa shifts and provide valuableinsight into the possible molecular origins of theinteractionsthat perturb pKa values, there is a tendency tooverestimate the magnitude of the shifts and their saltdependence. Interestingly, the shapes of both the calculated andobserved transitions are often morecomplex than expected for a simple titration, suggesting thatpKa values at many sites are changingduringthe transition. Differences between predicted and experimentalpKa values and titration profiles forsomeresidues may be due to as yet uncharacterized structural changes at theextremes of pH.