Structure of The Z Disk of Sectioned Bee Flight Muscle
Information from oblique thin sections and from 3-D reconstructions of tilted transverse thin sections has been combined to determine the 3-D structure of the honeybee flight muscle Z disk at 7øÅ resolution. The overall symmetry and structure of the Z disk and its relationship to the rest of the myofibril have been determined by tracing filaments and connecting elements on electron images of oblique sections which have been enhanced by a local crystallographic averaging technique .The 3-D structure of the central region of the Z disk of honeybee flight muscle has been determined by crystallographic 3-D reconstruction from electron micrographs of tilted thin sections. The reconstructions show a complex network in which actin filaments terminate and are crosslinked together (Figure 1); a number of structural domains are resolved in the network.The central region of the Z disk contains two sets of overlapping actin filaments of opposite polarity, which originate in the sarcomeres adjacent to the Z disk, and connections between these filaments. The filaments are deflected by the attachment of crosslinks; spacings between filaments change by over 1øøÅ during their passage through the Z disk. Each actin filament is linked by connecting structures to four filaments of opposite polarity and two filaments of the same polarity.