Solvent proton relaxation of aqueous solutions of the serum proteins alpha 2-macroglobulin, fibrinogen, and albumin

The longitudinal, transverse, and spin-locked rotating frame relaxation rates have been measured for water protons in aqueous solutions of the human serum proteins albumin, fibrinogen, and alpha 2-macroglobulin in the physiological concentration range below 50 g/liter, corresponding to an upper limit for molarity of 725, 147, and 69 microM, respectively. The linear concentration dependence of all the relaxation rates measured at 100 MHz was used to provide the molar sensitivities of each relaxation process for each of the protein solutes. Both the solute dependence and the relaxation-process dependence of the molar sensitivities have been analyzed in terms of a model that has emerged from previous R1 dispersion measurements. This analysis demonstrates consistency between our data and that model for the active motions and their motional rates