title: Acid dissociation constant and apparent nucleophilicity of lysine-501 of the alpha-polypeptide of sodium and potassium ion activated adenosinetriphosphatase.
abstract: A combination of competitive labeling with [3H]acetic anhydride [Kaplan, H., Stevenson, K. J., & Hartley, B. S. (1971) Biochem. J. 124, 289-299] and immunoaffinity chromatography is described that permits the assignment of the acid dissociation constant and the absolute nucleophilicity of individual lysines in a native enzyme. The acid dissociation constant of lysine-501 of the alpha-polypeptide in native (Na+ + K+)-ATPase was determined. This lysine had a normal pKa of 10.4. The rate constant for the reaction of the free base of lysine-501 with acetic anhydride at 10 degrees C is 400 M-1 s-1. This value is only 30% that for a fully accessible lysine in a protein. The lower than normal apparent nucleophilicity suggests that lysine-501 is hindered from reacting with its intrinsic nucleophilicity by the tertiary structure of the enzyme and is consistent with its location within a pocket that forms the active site upon the surface of the native protein.
authors.affiliation: Department of Chemistry, University of California at San Diego, La Jolla 92093.
authors.forename: K Y
authors.initials: KY
authors.lastname: Xu
mesh_terms: D000085:Acetates / Q000378:metabolism*; D000089:Acetic Anhydrides / Q000378:metabolism*; D000107:Acetylation; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000201:enzymology; D002846:Chromatography, Affinity; D004285:Dogs; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008239:Lysine / Q000302:isolation & purification; D008433:Mathematics; D008962:Models, Theoretical; D010649:Phenylalanine / Q000302:isolation & purification / Q000031:analogs & derivatives; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014316:Tritium
chemical_list: D000085:Acetates; D000089:Acetic Anhydrides; D014316:Tritium; D010649:Phenylalanine; D000254:Sodium-Potassium-Exchanging ATPase; D008239:Lysine; C044228:N-acetylphenylalanine