Polarized neutron scattering by polarized protons of bovine serum albumin in deuterated solvent

Bovine serum albumin (BSA) was dissolved in a mixture of deuterated glycerol and heavy water. The clusters formed by the 3300 proton spins in each BSA molecule were dynamically polarized up to P = 40%. Spin-contrast variation in small-angle neutron scattering was studied at several target polarizations. Zero contrast, and hence minimum polarized neutron small-angle scattering, is expected at P_H = 60% from extrapolation of present data. The three basic scattering functions of spin-contrast variation look very similar because the shape of the BSA molecule and its proton distribution are congruent. Neutron small-angle scattering of BSA is similar to X-ray small-angle scattering at room temperature, indicating no deterioration of the molecular structure of BSA on solidification.