Electron microscopy of frozen hydrated biological specimens.

The use of frozen hydrated specimens for molecular structure determination is limited primarily by radiation damage. The radiation damage effect in frozen hydrated catalase crystals has been measured in terms of the loss of electron diffraction. The results show an improvement for this type of specimen relative to wet hydrated or to glucose embedded catalase crystals at room temperature. Bright field images of unstained, frozen hydrated catalase crystals extend to a resolution of 11.5 A. The image resolution is presently limited by design problems with the liquid nitrogen cooled specimen stage. Rather high contrast is present in these images of unstained biological material, presumably due to the 30% difference in mass density between ice and protein. The improved resistance to radiation damage also makes it possible to give better statistical definition to the image, thereby making the image features easier to see.

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