Abstract
Islet tissue minces from the fish Lophius piscatorius have been incubated with proline-C14 for 8 hr. and with proline-H3 for 15 or 30 min. at 17[degree]C. After incubation, the minces were combined, insulin was extracted, purified, and separated into 3 peptides, each containing 1 proline residue. The 3 proline residues were isolated and their H3/C14 ratios determined. From these radioactivity of values and from knowledge of the positions of proline in the chains, evidence was obtained for the conclusion that the 2 constituent chains of insulin are synthesized separately.