The substructure of crystalloids in secretory granules of dog pancreatic islet B cells


  • Mitsuo Machino

    1. Department of Anatomy, The Pennsylvania State University, The Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033
    Current affiliation:
    1. Department of Anatomy, Kyoto Prefectural University of Medicine, Kamikyo-Ku, Kyoto, Japan
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    • Fellow, China Medical Board, March 1969 – March 1970

  • This research was supported in part by United States Public Health Service Research grant AM 11407.


The B cells of dog pancreatic islets were studied by electron microscopy. The crystalloid core of secretory granules in B cells is unique. The crystallization of the secretory granule core appears to be accomplished in the Golgi apparatus. The square or hexagonal network with a periodicity of 30–60 Å that is produced suggests that the unit cell is either hexagonal or rhombohedral. The electron opaque dots which constitute the periodic densities may represent the insulin molecule itself in a crystalloid array.