The incorporation of tritium-labelled amino acids into insulins in rat pancreas in vitro

Abstract

When [H3] leucine is in-cubated with pancreas segments in a bicarbonate-buffered medium containing glucose there is a substantial uptake of amino acid from the medium, with a rapid incorporation of tritium into an acidic-ethanol-soluble fraction of the pancreatic proteins. Incorporation into this fraction appears to be inhibited by addition of 2,4-dinitrophenol (0.25 mM) to the medium. A-chain made from rat insulins appears to be labelled when isolated from rat-pancreas segments which had been incubated with [H3] leucine or [H3]-isoleucine. Incorporation of labelled leucine into A-chain is inhibited by addition of 2,4-dinitrophenol to the medium. When rat-pancreas are incubated with [H3] leucine, B-chain from one of the insulins is also labelled, though virtually no label appears in the B-chain isolated from pancreas which had been incubated with [H3] isoleucine, in accordance with the postulated structures for rat insulins. These results argue against some nonspecific form of incorporation of the amino acids into rat insulins when amino acids are incubated with rat pancreas in vitro.