Transport of bovine chymotrypsinogen into rabbit pancreatic cells.

LIEBOW, C., AND S. S. ROTHMAN. Transport of bovine chymotrypsinogen into rabbit pancreatic cells. Am. J. Physiol. 226(5) : 1077-1081. 1974.-Chymotrypsinogen uptake was measured into slices of rabbit pancreas incubated in bovine chymotrypsinogen-3H and albumin J311. Chymotrypsinogen uptake was 16 times greater than that for albumin. Chymotrypsinogen-3H was not readily “chased” by washing in cold chymotrypsinogen. Exogenous enzyme was found to be distributed within the cell like endogenous enzyme; i.e., zymogen granules (ZG) had the highest specific radioactivity (SRA). Enzyme entered the cytoplasm more rapidly than the ZG. By 60 min, both fractions approached tracer equilibration (while mitochondrial and microsomal fractions were still far below bath SRA), suggesting that these enzyme pools exchanged relatively freely with media. The existence of enzyme equilibrium between bath-cytoplam-ZG suggests bidirectional processes, at least one of which appears to involve the transport of proteins across plasma membrane by nonexocytotic mechanisms.