STUDIES ON INSULIN BIOSYNTHESIS : Subcellular Distribution of Leucine-H(3) Radioactivity During Incubation of Goosefish Islet Tissue

Islet tissue from the goosefish (Lophius piscatorius) was incubated in the presence of leucine-H(3). The tissue was then separated into subcellular fractions and the radioactivity determined in total acid alcohol-soluble proteins, insoluble proteins, and insulin. At any time, microsomal protein had a higher activity than secretion granule protein. Pulse-chase experiments further suggest the microsomes as primary sites of protein synthesis. The data are evidence for microsomal synthesis of insulin and for its subsequent transfer into the secretion granules.