SIALYLTRANSFERASE ACTIVITY IN FR3T3 CELLS TRANSFORMED WITH RAS ONCOGENE - DECREASED CMP-NEU5AC-GAL-BETA-1-3GALNAC ALPHA-2,3-SIALYLTRANSFERASE

We have investigated the activity of CMP-Neu5Ac:Galbeta1-3GalNAc alpha -2,3-sialyltransferase (EC 2.4.99.4) in FR3T3 cells transformed by the Ha-ras oncogene in which we have previously demonstrated the higher e xpression of the beta-galactosidase alpha-2,6-sialyltransferase (EC 2. 4.99.1) [21]. We demonstrate that the presence of the activated ras ge ne decreases the activity of this specific alpha-2,3-sialyltransferase fourfold. According to the kinetic parameters and to mixing experimen ts, we can assume that this decreased enzymatic activity reflects a de crease in the number of active O-glycan alpha-2,3-sialyltransferase po lypeptides in ras-transformed cells. However, no change in the binding of Peanut agglutinin was observed on the cell surface of ras-transfor med FR3T3 suggesting that no change in the sialylation of O-glycan cor e 1 appeared in these cells, although the activity of the alpha-2,3-si alyltransferase was decreased.