A DETAILED STUDY OF THE ACTIVE SITE OF RUBISCO BY X-RAY CRYSTALLOGRAPHY Anthony P. Duff*, T. John Andrews** & Paul M. G. Curmi*, *IBiS, School of Physics, The University of New South Wales, NSW 2052, Australia **Research School of Biological Sciences, The Australian National University, Canberra, ACT 2601, Australia.

We are creating new complexes with rubisco by co-crystallisation to further study its complex reaction. Rubisco is very well known amongst plant enzymes, for its abundance (50% soluble leaf protein), for its inefficiency (reaction rate 2 per second), and for the many years that many groups worldwide have put into its study. Despite previous studies, the active site, and protein as a whole is not satisfactorily understood. That is why we are intent on completing probably the most difficult task yet to be done - the co-crystallisation of rubisco complexed with new intermediate analogues, so as to complete a set of snapshots of the five-step reaction. Crystallisation of new complexes has been achieved, and optimisation and x-ray diffraction is continuing. Electron density has been calculated in one case, giving us more definite knowledge of the movements of an important loop. Differences and similarities in crystallisation of different reaction states suggest some general properties of the enzyme. We are also eager to discuss difficulties, techniques and inventions in the methods of purification, crystallisation, and wet and cryo x-ray diffraction.