Sub-Golgi distribution in rat liver of CMP-NeuAc GM3- and CMP-NeuAc:GT1b alpha 2----8sialyltransferases and comparison with the distribution of the other glycosyltransferase activities involved in ganglioside biosynthesis.
Using a sucrose density gradient fractionation of a highly purified Golgi apparatus from rat liver, we determined the sub-Golgi distribution of CMP-NeuAc:GM3 ganglioside alpha 2----8sialyltransferase (GM3-SAT) and CMP-NeuAc:GT1b ganglioside alpha 2----8sialyltransferase (GT1b-SAT), in comparison with that of the other glycosyltransferase activities involved in ganglioside biosynthesis. While GM3-SAT was recovered in several density fractions, GT1b-SAT was mainly found on less dense sub-Golgi membranes; this indicates that these two activities are physically separate. Moreover, with regard to the monosialo pathway, CMP-NeuAc:lactosylceramide alpha 2----3sialyltransferase, UDP-GalNAc:GM3 ganglioside beta 1----4N-acetylgalactosaminyltransferase, UDP-Gal:GM2 ganglioside beta 1----3galactosyltransferase, and CMP-NeuAc:GM1 ganglioside alpha 2----3sialyltransferase were resolved from more dense to less dense fractions, respectively. In the disialo pathway, UDP-GalNAc:GD3 ganglioside beta 1----4N-acetylgalactosaminyltransferase, UDP-Gal:GD2 ganglioside beta 1----3galactosyltransferase and CMP-NeuAc:GD1b ganglioside alpha 2----3sialyltransferase co-distributed with the corresponding activities of the monosialo pathway. These last results indicate that many Golgi glycosyltransferases involved in ganglioside biosynthesis are localized in the order in which they act.
Trinchera
M
M
Department of Medical Chemistry and Biochemistry, Medical School, University of Milan, Italy.
Pirovano
B
B
Ghidoni
R
R
D000116:Acetylgalactosamine; D000818:Animals; D002240:Carbohydrate Sequence; D002451:Cell Compartmentation; D002499:Centrifugation, Density Gradient; D005700:Galactosyltransferases / Q000378:metabolism; D005732:Gangliosides / Q000096:biosynthesis*; D006056:Golgi Apparatus / Q000201:enzymology* / Q000648:ultrastructure; D006602:Hexosyltransferases / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D051381:Rats; D012799:Sialyltransferases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
D005732:Gangliosides; D005700:Galactosyltransferases; D006602:Hexosyltransferases; D012799:Sialyltransferases; D000116:Acetylgalactosamine