Neutron and ion beams in biological research

Summary

Neutron reflectometry is an excellent technique to determine the structure of a protein layer adsorbed at a solid interface. The use of contrast-variation makes it possible to highlight the adsorbed protein layer. The neutron scattering lengths of D and H have opposite signs. By choosing the H₂O/D₂O ratio, the scattering length density can be made equal to that of the adsorbing substrate. To determine the scattering length density of protein, both its volume and its scattering length in solution is needed. To calculate the scattering length, the H-D exchange of the labile protons of the protein should be taken into account. For monitoring the H-D exchange, electrospray ionization mass spectroscopy (ES⁺I-MS) was applied. We show that ES⁺I-MS is the appropriate technique for quantitative analysis of the H-D exchange. We compare the experimental results for the exchange in lysozyme and &bgr;-casein with theoretical calculations.