THE BINDING SITES OF KRYPTON AND XENON IN PROTEINS : A SURVEY OF A TENS OF COMPLEXES. Thierry Prangé, Marc Schiltz and Roger Fourme. LURE, Bât. 209d, Université Paris-Sud, 91405 Orsay Cedex, France.

It is now well established that the noble gases xenon and krypton bind to numerous proteins through weak Van der Waals interactions. In about fifty percent of the examined cases, the sites are sufficiently well defined (in terms of occupancy factors and phasing power) to be used as highly isomorphous heavy atom derivatives in MIR or SIRAS techniques (several examples will be presented during this meeting). The binding site environments of a set of ten proteins including elastase, cutinase, subtilisin, collagenase, lysozyme, urate oxidase, etc.. are analysed in terms of polar/hydrophobic interactions and close contacts to feature out a general prediction for the binding under moderate gas pressure (4 to 40 bar).