ISOLATION AND PROPERTIES OF SECRETORY GRANULES FROM RAT ISLETS OF LAN GERHANS I. Isolation of a Secretory Granule Fraction

A method has been devised for the isolation of a secretory granule fraction from isolated rat islets of Langerhans . The islets were homogenized in buffered sucrose, and the homogenate was separated into nuclear, mitochondrial, secretory granule, and microsomal fractions by differential centrifugation . The secretory granule fraction was purified by differential centrifugation in discontinuous sucrose density gradients . A greater degree of purification could be achieved by the use of two successive gradients of this type, although the final yield was greatly reduced . Biochemical and morphological characterization of the fractions was obtained; the secretory granule fraction contained both insulin and glucagon . The limiting membranes of the granules remained intact and the general appearance of the granules was similar to that seen within the whole islet cells .