Ectoglycosyltransferase Activities During Neuronal Differentiation in Cell Cultures
It is generally admitted that glycosyltransferases and the synthesis machinery of glycoconjugates are localized in the intracellular membrane structures such as the endoplasmic reticulum (Cook et al. 1965), Golgi apparatus (Schachter et al. 1970; Fleischer et al. 1969) and mitochondrial membranes (Bosman 1971; Broquet et al. 1975). Recently several reports concluded that glycosyltransferases also exist at the cell curface with their active sites exposed to the extracellular space (see for review Shur and Roth 1975; Cacan et al. 1976). The methods applied for detection of these ectoenzymes were direct enzymatic assays of intact cells or membranes as well as immunocytochemistry using antisera against glycosyltransferases and autoradiography (for review see Shur and Roth 1975; Shur 1982). Most frequently the addition of a radiolabeled sugar from a sugar nucleotide to the plasma membrane of intact cells was used to test ectoglycosyltransferase activities. According to the results obtained, the presence of ectoglycosyltransferase activities was reported at the cell surface of lymphocytes (Cacan et al. 1976; Hoflack et al. 1979), leukemic cells (Bernacki and Porter 1978), cultured nerve cells from chick embryo retinas (Roth et al. 1971), embryonic liver (Arnold et al. 1973), sperm (Shur and Bennet 1979), teratocarcinoma cells (Shur and Roth 1975; Shur 1982) and migrating mesenchymal cells (Hakomori 1981; Johnson 1977).
KeywordsSugar Hydrolysis Dopamine Sarcoma Galactose
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