Lactosylceramide synthesis

Butyrate treated Hela cells (2) and KB cells showed marked increases in the amounts of G 3 gangliosides and elevated levels of the enzyme, CMP sialic acid lactosylceramide sialosyltrans-ferase, required for its synthesis. 

HeLa cells were cultured for 24 hr with (open bars) and without (closed bars) 5 mM sodium butyrate, harvested, and assayed for indicated enzyme activity. A GM3-sialidase activity assayed with GM3 specifically labeled with [,iC]- N-acetylneuraminic acid as substrate ("14JJ. B Sialyltrasferase activity assayed with CMP-[, acetylneuraminic acid and lactosylceramide as substrates, and synthesis of labeled GM3 determined (17). Data... 

Very little of 7T H7-galactose precursor was converted to a glucocerbroside or to a lactosylceramide under these culture conditions (21). The activities of the sulfotransferase and galactosyltransferase, enzymes responsible for the synthesis of the myelin-associated sulfo- and glycolipids, were also measured at different days in culture (fig. 4). The activities of these enzymes in homogenates of cells derived from the 15 day embryo were relatively low at 8 days but increased until reaching... 

Y. Harada, T. Murata, K. Totani, T. Kajimoto, S. Md. Masum, Y. Tamba, M. Yamazaki, and T. Usui, Design and facile synthesis of neoglycolipids as lactosylceramide mimetics and their transformation into glycoliposomes, Biosci. Biotachnol. Biochem., 69 (2005) 166-178. 

Fukumoto S, Miyazaki H, Goto G, Urano T, Furukawa K, Furukawa K (1999) Expression cloning of mouse cDNA of CMP-NeuAc Lactosylceramide a2,3-sialyltransferase, an enzyme that initiates the synthesis of ganglio-sides. J Biol Chem 274 9271-9276... 

The movement of sphingolipids between elements of the Golgi has been monitored in reconstituted preparations from mutant Chinese hamster ovary cells defective in either the synthesis of lactosylceramide or the attachment of sialic acid to the latter (B. Wattenberg,... 

The enzyme catalyzing reaction 6 was also found in the brain of young rats. In addition to lactosylceramide, lactose was also claimed to serve as a substrate. Care is, however, needed in interpreting these results, because chick brain is known to contain a fourth sialyl transferase that utilizes various jS-D-galactosides as acceptors, and which is, presumably, involved in glycoprotein synthesis. ... 

Bovine milk contains an enzyme, in soluble form, which catalyses the transfer of D-galactose from UDP-D-galactose to D-glucosylceramide. The synthesis of the product, lactosylceramide, was inhibited by the presence of a-lactalbumin. Lactosylceramide was also an effective acceptor of D-galactose, but neutral glycosphingolipids or gangliosides were very poor receptors. 

This large and important group of glycolipids is derived from lactosylceramide and the pathways involved are, perhaps, the best understood of any concerned in the synthesis of complex saccharides. Many of these transfers are also found in glycoproteins, where they appear to be brought about by the same enzymes that act on the glycolipids — or, at least, enzymes that are under almost exactly the same genetic control (see Section 5B above). 

Scheme 8. Synthesis of lactosylceramide from acyl-protected lactose via anomeric O-alkylation.

P4-GalT VI has been identified as a lactosylceramide synthase [175]. Whether it acts on substrates other than glucosylceramide has not been determined. Finally, the p4-GalT involved in the first step of the synthesis of the GlcA(pi-3)Gal(pi-3)Gal(pi-4)Xyl core region of proteoglycans has recently been cloned and seems to be another member of this family [176, 195]. It is proposed to refer to this enzyme as p4-GalT VII. 

Liu, Y Bittman, R. Synthesis of fluorescent lactosylceramide stereoisomers. Chem. Phys. Lipids 2006,142,58-69. 

The SAT that catalyzes the synthesis of sialyllactose was first detected in rat mammary tissue by Roseman and his co-workers (Jourdian et al., 1963 Carlson et al., 1973a). In fact, this was the first SAT to be characterized in an animal system, being detected later in embryonic chicken brain (Kaufman and Basu, 1966). However, the SAT activities that catalyze the transfer of sialic acid to lactose and to lactosylceramide appear to be different from the latter by all kinetic parameters (S. Basu, 1966 Kaufman and Basu, 1966 M. Basu et al., 1987 S. C. Basu, 1991). In addition to CMP-NeuAc lactose a2-3 sialyltransferase, CMP-NeuAc lactosamine a2-6 sialyltransferase (ST6N) was first characterized by Roseman and his co-workers (Bartholomew et al., 1973) from colostrum. The ST6N enzyme activity is ubiquitous and was purified by Hill and his associates... 

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