RELEASE OF SIALYLTRANSFERASES FROM RAT-LIVER GOLGI MEMBRANES BY A CATHEPSIN D-LIKE PROTEINASE - COMPARISON OF THE RELEASE OF GAL-BETA-1-4GLCNAC-ALPHA-2-6 SIALYLTRANSFERASE, GAL-BETA-1-3(4)GLCNAC-ALPHA-2-3 SIALYLTRANSFERASE AND LACTOSYLCERAMIDE ALPHA-2-3 SIALYLTRANSFERASE (SAT-1)

The activities of Gal beta 1-3(4)GlcNAc alpha 2-3 sialyltransferase an d SAT-1 were measured in rat liver Golgi in inflammation; both enzymes decreased by about 50%. This compares with increases of about 3-fold for the Gal beta 1-4ClcNAc alpha 2-6 sialyltransferase. All three sial yltransferases were released from disrupted Golgi membranes by incubat ion at reduced pH which activates an endogenous cathepsin D which is b elieved to be the lysosomal enzyme. Pepstatin A was found to block the release of all three sialyltransferases providing support for the rol e of cathepsin D as the proteinase that clips the catalytic portions o f the enzymes from their membrane anchor and stem regions.