Chemical properties of the N-termini of human haemoglobin.
The chemical properties, namely pK and reactivity, of the N-termini of oxyhaemoglobin and deoxyhaemoglobin toward acetic anhydride and 1-fluoro-2,4-dinitrobenzene (Dnp-F) were determined by the competitive-labelling approach [Kaplan, Stevenson & Hartley, (1971) Biochem. J. 124, 289-229; Duggleby & Kaplan (1975) Biochemistry 14, 5168-5175]. At physiological pH and temperature, the valine-1 alpha and valine-1-beta amino groups had unusually  low pK values, but showed only minimal changes in their pK values on deoxygenation. Between pH 7.5 and pH 8.0 a deviation was observed in the pH-reactivity profiles and the apparent pK values became markedly pH-dependent. It was found that Dnp-F, but not acetic anhydride, had an abnormally high reactivity toward the N-termini. It is concluded that the valine-1 alpha and valine-1 beta N-termini make little or no contribution to the alkaline Bohr effect at physiological pH values. The high reactivity toward Dnp-F is attributed to an interaction or binding near the N-terminal region, and the discontinuity in the pH-reactivity profile at moderate alkaline pH values to a conformational change which alters the environment of these groups.
D000089:Acetic Anhydrides / Q000378:metabolism; D000595:Amino Acid Sequence; D002250:Carbon Radioisotopes; D004139:Dinitrofluorobenzene / Q000378:metabolism; D006441:Hemoglobin A / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010108:Oxyhemoglobins / Q000378:metabolism; D011487:Protein Conformation; D014316:Tritium
D000089:Acetic Anhydrides; D002250:Carbon Radioisotopes; D010108:Oxyhemoglobins; D014316:Tritium; C031800:acetic anhydride; D006441:Hemoglobin A; C029774:oxyhemoglobin A; D004139:Dinitrofluorobenzene