Biochemical and biophysical characterization of insulin granules isolated from rat pancreatic islets by an iso-osmotic gradient.

The size and polydispersity of insulin granules isolated from rat pancreatic islets by centrifugation on a linear iso-osmotic gradient (300 mosM) have been characterized by quasi-elastic light scattering and photon correlation spectroscopy. The separation of granules by the linear gradient technique was compared directly to isolation on discontinuous gradients of hypertonic sucrose (300-1950 mosM) and the greater efficiency of separation assessed by parallel measurements of protein, insulin, cytochrome oxidase and beta-glucuronidase. Granules isolated from pancreatic beta-cells had a mean particle diameter of 342 nm, buoyant density of 1.104, hydrated mass of 23 femtograms and maximal insulin content of 8-9.6 . 10(5) molecules per granule.