title: Cell-surface glycosyltransferases in cultured fibroblasts: increased activity and release during serum stimulation of growth.
abstract: Cell-surface galactosyltransferase was studied in suspensions of intact baby hamster kidney fibroblasts with both endogenous and exogenous glycoprotein acceptors. The cell-surface location of galactosyltransferase was demonstrated in experiments with the enzyme modifier alpha-lactalbumin, which does not enter the cell. The addition of alpha-lactalbumin to the assay medium for galactosyltransferase resulted in accumulation of lactose in the medium but not in the cells. There was no detectable hydrolysis of UDP-galactose to free galactose by these cells, nor did a 100-fold molar excess of free galactose inhibit cell-surface galactosyltransferase. There was a marked increase in specific activity of cell-surface exogenous galactosyltransferase in serum-stimulated as compared to resting fibroblasts. Dividing but not resting fibroblasts released galactosyltransferase, but not sialyl- or fucosyltransferase, in soluble form into the tissue culture medium. The release of galactosyltransferase was greater from virally transformed than from nontransformed fibroblasts.
mesh_terms: D001769:Blood; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology*; D002471:Cell Transformation, Neoplastic; D003470:Culture Media; D005347:Fibroblasts / Q000201:enzymology; D005700:Galactosyltransferases / Q000378:metabolism*; D007768:Lactalbumin / Q000378:metabolism; D007785:Lactose / Q000096:biosynthesis; D011120:Polyomavirus
chemical_list: D003470:Culture Media; D007768:Lactalbumin; D005700:Galactosyltransferases; D007785:Lactose