Sialyltransferases with Glycolipid Substrates

The controversy still existing about the biosynthesis of gangliosides in various tissues has not been resolved by the study of glycosyltransferase enzymes. The 

E (Neu5Ac)2lI Neu5AcGgOse4Cer E Neu5AcIt Neu5Ac)2GgOse4Cer D (Neu5Ac)3GgOse/ Cer 

G[ (Neu5Ac) (Neu5Ac)2GgOse/ Cer Neu5AclI ( Neu5Ac)3GgOse Cer 

Lactosylceramide sialyltransferase (step 2) was originally detected in embryonic chicken brain (Kaufman ef al. 1968), has also been found in calf brain (Pretic al 

The transfer of NeuSAc leading to IV3Neu5AcIPNeu5AcGgOse4Cer (step 7) is distinct from step 2 sialyltransferase (Kaufman et al. 1968, Mestrallet et al. 1977). This sialyltransferase has also been demonstrated in rat brain by Yip(1973) and in rabbit neurohypophysis by Clarke and Mulcahey (1976). Step 8 

---

The specific induction of de novo synthesis of sialyltransferase for glycolipid substrates by fatty acids has been studied in detail, and a hormonal regulation discussed by Fishman et al. (1976). Morphological changes in HeLa cells could be associated with the specific induction of LacCer sialyltransferase (IPNeu5AcLacCer formation), which was blocked by protein synthesis inhibitors. 

The substrate requirements, linkage specificity, and kinetic mechanism of an q -2,3-sialyltransferase have been compared with an a-2,6-sialyltransferase from porcine submaxillary mucin.The former enzyme will specifically modify glycoproteins and glycolipids which contain 2-acetamido-2-deoxy-3-O S-D-galactosyl-D-galactose sequences. The only acceptor substrates reported for the a-2,6-sialyltransferase are those glycoproteins containing the structure (58). ... 

---