Pulsed nuclear magnetic resonance studies on 23Na, 7Li and 35Cl binding to human oxy- and carbon monoxyhaemoglobin

Abstract

Pulsed nuclear magnetic resonance studies of the longitudinal ( T 1) and transverse ( T 2) quadrupolar relaxation times of 7Li, 23Na, 35Cl ions in the absence and presence of human oxy- and carbon monoxyhaemoglobin have been used to investigate the interaction of the ions and the macromolecule. The relaxation data show that Cl − interacts strongly with the haemoglobin but provide no evidence for binding of Na + up to concentrations of 0.5 m. In the case of Li +, evidence for interaction is obtained at concentrations of about 0.1 m. The dependence of relaxation rate on frequency was followed over a limited frequency range in an attempt to separate the effects of correlation times and exchange rates of the bonded ions on the relaxation. In the case of Cl −, an upper limit for the mean lifetime divided by the number of sites can be set at about 1 × 10 −6 second, and a lower limit at about 1 × 10 −8 second.