Message-Id: <199701281434.JAA04875@chem.bu.edu>
Date: Tue, 28 Jan 1997 09:36:46 +0000
From: laursen@bu.edu (Richard Laursen)
Subject: Re: pKa of Asn sidechain
To: Recipients of ABRF List <abrf@aecom.yu.edu>
>I have been trying without success to find out the pKa of asparagine's
>side chain nitrogen. Is there a good site, electronic or printed, for
>this and similar information?
>
>Mike Klein
>Protein Design Labs, Inc.
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I don't know if anyone has ever measured the pKa of the side chain of
asparagine, since it is an amide and amide pKa's are not easy to determine,
but it must be close to that of acetamide. I have found two values for
acetamide:
pKa = -0.5
(Albert and Serjeant, "Ionization Constants of Acids and Bases," Wiley,
1962, p. 141)
J. Hall, J. Am. Chem. Soc., 52, 5115 (1930).
Lunden, Z. physik. Chem., 54, 532 (1906)
pKa = -1.40
(Yukawa, "Handbook of Organic Structural Analysis", Benjamin, 1965, p. 590)
J.T. Edward, S.C.R. Meacock, J. Chem. Soc., 2000 (1957).
G. Briezleb, Z. Elektrochem., 53, 350 (1949)
So you have your choice. I think it would be safe to say that the pKa of
the asparagine amide side chain is around -1.0 +/- 0.5. From a biochemical
point of view, the amide group is neutral.
Richard A. Laursen
Department of Chemistry
Boston University
590 Commonwealth Ave.
Boston, MA 02215
Tel (617) 353-2491; FAX (617) 353-6466
email: <laursen@bu.edu>