Localization of copper-zinc superoxide dismutase in the endocrine pancreas

Immunoelectron microscopy and cellular fractionation on sucrose density gradients have been used to examine the intracellular distribution of copper-zinc superoxide dismutase (SOD) in the canine and rat endocrine pancreas. Using rabbit anti-canine copper-zinc SOD as the primary antiserum, immunostaining in canine beta and non-beta islet cells was significantly greater than that in serial sections of the same islet incubated with preimmune serum from the same rabbit. Within the cells, immunostaining was associated with spherical and crystalloid granules as well as with the cytoplasm. Radioimmune assays of cellular fractions or rat islet-cell preparations showed that the granule-rich fraction containing large amounts of insulin was also rich in SOD. This interesting observation of association of SOD with hormone-containing granules suggests that SOD may play a role in protecting these oxidation-sensitive proteins.