Abstract
Granules containing melanophore stimulating hormone were separated from bullfrog pars intermedia by differential centrifugation and sucrose gradient centrifugation. These granules were present in the supernatant after centrifugation at 650g for 15min and were sedimented by centrifugation at 11, 000g for 15min. Sucrose gradient centrifugation of this fraction revealed that MSH activity was present in granules having a density equivalent to 1.6-1.7M sucrose solution and a diameter 1, 500-3, 000Å. From their size and structure, it is concluded that MSH granules are the small electron-dense granules and not the large colloidal granules observed in electron micrographs of the pars intermedia.
