Evaluation of beam damage in catalase crystals observed in vitrified sections

Abstract

It was a major breakthrough that Gleaser [1] quantitatively determined beam damage by measuring the fading of electron diffraction spots in organic crystal. The method was soon extended to catalase crystal, which became a kind of working horse for quantitative evaluation of specimen preparation methods [2,3]. For such purpose, catalse crystals are well suited because they can be grown slowly into very thin platelet. The crystal lattice of the platelet is tetrahedral with lattice constant of 6.9 nm and 17.4 nm in the length and width respectively and 20.6 nm in the thickness. Cryo-electron microscopy of vitreous sections (CEMOVIS) is a technique which has recently reached maturity after decades-long development [4,5]. What is shown with CEMOVIS is surprizingly different from what is used to be seen with conventional electron microscopy. And it seems that a better resolution is generally obtained. However, the quality of the recorded images and the plethora of significant information contained over the thickness of a section call for 3D reconstruction of the section. This can be achieved with the remarkable method of computerized electron tomography (CET). It requires that a large number of images of the same region are recorded in different orientations. Therefore, beam damage is the major limitation of the method.