Primary radiation damage of protein crystals by an intense synchrotron X-ray beam

X-ray radiation damage of a lysozyme single crystal by an intense monochrom atic beam from a third-generation radiation source at the Advanced Photon S ource has been studied. The results show that primary radiation damage is l inearly dependent on the X-ray dose even when the crystal is at cryogenic t emperatures. The existence of an upper limit for the primary radiation dama ge was observed. Above the threshold of approximately 1 x 10(7) Gy, excessi ve damage of the crystal develops which is interpreted as the onset of seco ndary and/or tertiary radiation damage. This upper limit of X-ray dose is c ompared with Henderson's limit [Henderson (1990). Proc. R. Soc. London, B24 1, 6-8], and its implication for the amount of useful X-ray diffraction dat a that can be obtained for crystals of a given scattering power is also dis cussed.