Localization of [¹²⁵I]-insulin in subcellular particles of perfused rat liver

Rat livers were cyclically perfused for 30 min at 23°C with physiological concentrations of [¹²⁵I]-insulin, the mitochondrial-lysosomal fraction was isolated and subjected to sucrose density gradient centrifugation. A peak of radioactive material, similar in size to native insulin, co-migrated with the peak of lysosomal marker enzyme on density gradients. The uptake of this material was blocked at low temperatures and Triton WR-1339 pretreatment failed to alter its distribution on the gradient. These findings indicate that the radioactive material in the peak represents [¹²⁵I]-insulin, (or large fragments) that is associated with vesicles which compare with lysosomes in density but differ in Triton-storing capability.