The Identification of Proinsulin-Synthesizing Polysomes in Fetal Bovine Pancreas

Abstract

Antiserum against bovine pancreatic RNase A was produced in the rabbit. (Fab′)2 fragments were prepared from the antiserum and were found to inhibit the degradation of rat liver polysomes by fetal bovine pancreatic supernatant which contained RNase activity. Using this anti-RNase preparation, we were able to obtain fetal bovine pancreatic polysomes which appeared intact. Radioimmunoassay of the polysomal fractions after sucrose density gradient centrifugation showed that insulin immunoreactivity was associated mainly with tetrasomes, pentasomes, and some larger polysomal aggregates, suggesting the participation of these polysomes in the synthesis of proinsulin. The possibility that a precursor larger than proinsulin might be involved in the synthesis of insulin was discussed.