Publications - 1999

We have examined the temperature-dependence of motions in a cryosolution of the enzyme glutamate dehydrogenase (GDH) and compared these with activity. Dynamic neutron scattering was performed with two instruments of different energy resolution, permitting the separate determination of the average dynamical mean-square displacements on the sub ~100 ps and sub ~5 ns timescales. The results demonstrate a marked dependence on timescale of the temperature profile of the mean-square displacement. The lowest temperature at which anharmonic motion is observed is heavily dependent on the time window of the instrument used to observe the dynamics. Several dynamical transitions (inflexions of the mean-squared displacement) are observed in the slower dynamics. Comparison with the temperature profile of the activity of the enzyme in the same solvent reveals dynamical transitions that have no effect on GDH function.

Nuclear waste storage strategies and the issues that they entail are presented and discussed. A brief discussion is also given of the role that transmutation techniques might play.

Understanding biological processes that occur in aqueous solution requires an understanding of the influence of the solvent. Thus we have a need to understand the nature of the water-biomolecule interface. Although a large body of structural information h as been built up through x-ray diffraction measurements on protein crystals, problems such as the effects of disorder, and the absence of information on specific hydrogen positions, has limited our ability to characterise this interface adequately. With t he possibility of high-resolution neutron measurements on well-ordered crystals of biomolecules, including at low temperature, some of these problems are being overcome. As a result of such work, we are now able for the first time to devise a set of struc tural principles that appear to rationalise both the apparently complex structure of the solvent at the interface, and its disorder.

The hydrophobic interaction is the name given to the driving force that brings non-polar groups together in aqueous solution. It is implicated in a range of biologically relevant processes, including membrane stability, protein folding, and enzyme-substrate interactions. Since the work of Frank and Evans over 50 years ago, this process is generally thought to be driven by the entropy released when 'ordered' water molecules in the hydration shell of the non-polar group are released to the bulk solvent. Using neutron scattering measurements, it is now possible to test the validity of this proposed molecular mechanism. We describe recent work on a range of alcohols that gives us both a picture of the hydration shell of non-polar groups, and allows us to assess any ordering of the hydration water with respect to the bulk solvent. The techniques are also beginning to give good structural information on solute organisation in aqueous solution, opening up a whole new field of liquid state crystallography.