Proinsulin biosynthesis in broken-cell preparations of islets of Langerhans.

1. Rabbit islets of Langerhans were disrupted by ultrasonic methods and the sonicated preparations were used to study proinsulin biosynthesis. 2. When [3h]leucine is incubated in such preparations, incorporation takes place into proinsulin, as evidenced by characterization on polyacrylamide gels, and by the conversion of this labelled material into insulin, by using trypsin. 3. The labelled proinsulin may also be purified by antiinsulin antibody bound to Sepharose. 4. With the broken-cell preparation it was shown that incorporation of leucine is accelerated by increasing the glucose content of the medium from 2mM to 16mM. However, 16mM-galactose or -sucrose did not stimulate incorporation significantly from basal values. This effect of glucose was abolished by cycloheximide. 5. The significance of these findings in relation to the mechanism of glucose stimulation of proinsulin biosynthesis is discussed.