The specific interaction between molecules is at the core of all biological processes. As an instrument, the analytical ultracentrifuge has been a core technology for characterizing the strength, shape and size of molecular complexes. For many biological questions, there is no substitute method for analyzing molecular interactions. However, the existing analytical ultracentrifuge is limited in the range of questions it can address. New and improved optical systems described in this proposal will overcome many of these limitations, thus allowing the analysis of trace materials, improving the precision of the measurements 100-fold and extending the analysis of concentrated mixtures by a factor of 10. Specifically, fluorescence, schlieren and turbidity detectors will be added. Improvements will be made to the computer systems that operate these detectors, and improvements will be made to the computer program used for interpreting sedimentation data
