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Isoelectric focusing of dansylated amino acids in immobilized pH gradientsThe 21 free amino acids commonly encountered in proteins have been transformed into 'carrier ampholyte' species by reacting their primary amino groups with dansyl chloride. These derivatives can thus be focused in an immobilized pH gradient covering the pH interval 3.1 to 4.1, except for arginine, which still retains a pI of 8.8. Due to their inherent fluorescence, the dansyl derivatives are revealed in UV light, with a sensitivity of the order of 2-4 ng/sq mm. All nearest neighbors are separated except for the following couples: Asn-Gln, Gly-Thr, Val-Ile and Cys-Cys2, with a resolving power, in a Delta(pI) scale, of the order of 0.0018 pH units. Except for a few cases (notably the aromatic amino acids), the order of pI values is well correlated with the pK values of carboxyl groups, suggesting that the latter are not altered by dansylation. From the set of pK(COOH)-pI values of the different amino acids, the pK of the tertiary amino group in the dansyl label has been calculated to be 5.11 + or - 0.06. Knowing the pK of the amino-dansyl and the pI of the excess, free dansyl label (pI = 3.34), a pK of 1.57 is derived for its sulfonic acid group.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Bianchi-Bosisio, Adriana
(Ospedale S. Carlo Borromeo Milan, Italy)
Righetti, Pier Giorgio
(Milano, Universita Milan, Italy)
Egen, Ned B.
(Milan Univ. Italy)
Bier, Milan
(Arizona, University Tucson, United States)
Date Acquired
August 13, 2013
Publication Date
March 1, 1986
Publication Information
Publication: Electrophoresis
Volume: 7
ISSN: 0173-0835
Subject Category
Chemistry And Materials (General)
Accession Number
Funding Number(s)
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