Investigation of the conformational lability of serum albumin macromolecules in aqueous solution by the NMR spin-echo method.

The complex proton spin-echo decay curve was recorded for human serum albumin (SA) solutions with different concentrations in normal and heavy water. The curve included three fast-decaying components for SA, in addition to the slow-decaying component for the water. The total amplitude of these three components roughly corresponded to the number of protons in the SA (with isotopic exchange taken into account); the component ratio remained constant at different concentrations and different temperatures between 4 and 39 degrees. The relatively slow-decaying protein component, which accounted for similar to 10% of the SA protons, was produced by the side chains of the protein. The presence of two other faster-decaying SA components with approximately equal amplitudes indicated that only about half of the remaining protons in the SA macromolecule are incorporated into the comparatively rigid globule, the other half belonging to groups with high conformational lability in aqueous solution. The activation energy for the aqueous component was close to that for pure water, while the activation energies for the protein components were roughly twice as large.