Biophysics and synchrotron radiation where the marriage fails. X-ray damage of lipid membranes and mesophases

The call for brighter synchrotron X-radiation sources for use in structural biology research is barely audible as we enter the new millennium. Our bri ghtest sources are already creating havoc when used at design specification s because of radiation damage. The time is long overdue to take stock of wh ere we are and where we wish to go with regards to using existing sources a nd to designing new ones. The problem of radiation damage is particularly s evere in studies involving kinetics and mechanism where cryotechniques are not always viable. Accordingly, we need to understand the very nature of ra diation damage and to devise means for minimizing it. This is the thrust of the current study as applied to lipid membranes and mesophases. Here, we r eport on two very different types of radiation damage. One involves a drama tic phase transformation and the other a disordering of lamellar stacking. How beam energy and dose/rate affect damage is also discussed. The work hig hlights the nature of the damage process and the need for additional studie s if we are to make most efficient use of an important resource, synchrotro n radiation.