| Summary: | Previous studies have demonstrated that there is a change in the molecular species specificity of CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase (LacCer alpha 2,3-ST) when the lipid composition of the Golgi membrane is altered (Kadowaki, Grant, and Williams, 1993. J. Lipid Res. 34: 905-914). To understand the basis of this phenomenon, the molecular species specificity of rat liver LacCer alpha 2,3-ST was determined under conditions in which the phospholipid class composition of the Golgi membrane was changed to resemble that of cultured mouse neuroblastoma NB2a cells, a cell line in which LacCer alpha 2,3-ST exhibits no molecular species specificity. The change in the lipid composition of the Golgi membrane was accomplished by incubating the Golgi membrane vesicles with nonspecific lipid transfer protein and a 10-fold excess of liposomes prepared with various proportions of purified rat liver lipids. The molecular species specificity of LacCer alpha 2,3-ST was also determined under conditions where the phospholipid molecular species composition but not the phospholipid class composition of the Golgi membrane was changed, and in which both the phospholipid class and molecular species compositions were changed by using liposomes prepared with lipids purified from a mouse brain tumor (ependymoblastoma). When using liposomes prepared with rat liver lipids, a change in the phospholipid class composition of the Golgi membrane to a composition similar to that of NB2a cells increased rather than decreased the molecular species specificity of rat liver LacCer alpha 2,3-ST.(ABSTRACT TRUNCATED AT 250 WORDS)
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