Cathepsin D-like activity in the release of Galβ 1-4GlcNAcα2-6sialyltransferase from mouse and guinea pig liver Golgi membranes during the acute phase response

Abstract

1. 1. Rat Galβ 1-4GlcNAcα2-6sialyltransferase (E.C. 2.4.99.1) is released from Golgi membranes by cleavage of a portion of the enzyme containing the active site from a membrane anchor, this effect was most dramatic during the acute phase response. The enzyme that cleaved sialyltransferase had the properties of cathepsin D was most active at pH 5.6 and was likely of lysosomal origin (lammers and Jamieson, 1988). 2. 2. The acute phase response of sialyltransferase in mouse and guinea pig was previously found to differ from that in the rat. Release of sialyltransferase from mouse and guinea pig Golgi membranes has now been studied in order to make a comparison with the rat system. 3. 3. Maximum release of sialyltransferase from mouse and guinea pig Golgi occurred at pH 4.6 and 5.2, respectively; like the rat a cathepsin D-like proteinase was responsible for release of both enzymes. 4. 4. Immunoblot analysis showed that membrane-bound rat and mouse sialyltransferase had M r 49,000, whereas the guinea pig enzyme had M r 42,000. The released form of the rat enzyme had M r 42,000, but released forms of mouse and guinea pig enzymes had M r 38,000 suggesting a different cleavage site for these two enzymes compared to the rate enzyme.