Determination by x-ray microscopy of the phases of the x-ray diffraction by macromolecular structures

摘要

The use of soft x-ray imaging is considered for the determination of the repeating macromolecular structure of biological fibers (e.g., collagen and muscle), within the available image resolution and subject to the effects of radiation damage. A comparison is made between the structure in sarcomere (2 $mu to 3 $mu long repeating unit) of striated muscle as seen directly by x-ray microscopy and as derived from published interpretations of x-ray diffraction data from whole muscle. The comparison shows that the loss by radiation damage of the ability of a muscle myofibril to contract is related to the loss of fine structure. Ways to minimize the effects of beam damage are discussed, including the use of images taken in phase, rather than amplitude contrast, and with photon energies above the `water window.'