Distribution of fluorescence decay times for 1-anilinonaphthalene-8-sulfonate in human oxyhemoglobin [A.sub.1b] solution

We have studied complex formation between molecules of the fluorescent probe 1-anilinonaphthalene-8-sulfonate (1,8-ANS) and the major form ([A.sub.1]) and a minor form ([A.sub.b]) of hemoglobin. The contribution of the long-lived component [f.sub.3] to the kinetic curves for fluorescence decay in [HbA.sub.1b] solutions is 0.021-0.036, which indicates a dramatic decrease (compared with [HbA.sub.1]) in the accessibility of the central cavity of [HbA.sub.1b] for binding 1,8-ANS. Disappearance of the long-lived component [f.sub.3] in the fluorescence decay kinetics of 1,8-ANS in [HbA.sub.1b] solutions in the presence of inositol hexaphosphate (IHP) suggests that the regulatory region of [HbA.sub.1b] is completely inaccessible for interaction both with the negatively charged molecules of the probe and with natural regulators of the transport function for this form of the heme protein.