Optical diffraction studies of myofibrillar structure.

We have used the techniques of optical diffraction and optical filtering to study electron micro­ graphs of myofibrils and of paracrystals of myofibrillar proteins. The optical diffraction patterns provide information about periodic structure in the micrographs, and sometimes may reveal periodicities not apparent to the eye. We compare the optical diffraction patterns with the X-ray diffraction patterns obtained from living muscle, and this comparison can assist our interpretation of both the X-ray diffraction patterns and the electron micrographs. The optical diffractometer we have used is essentially similar to those described by Taylor & Lipson (1964), and by Klug & DeRosier (1966). The apparatus incorporates several refine­ ments to facilitate operation. The recombining lens has a focal length, f , of about 1 m, and is placed so that the recombined image is formed at f and has the same size as the subject. The diffraction subjects are not usually the electron micrographs themselves but copies on film. The film is of more uniform optical thickness than the glass electron micrograph, and is less fragile. Moreover, a set of films of varying contrast can be made from one micrograph.