M. Pitto et al., DEPENDENCE OF RAT-LIVER CMP-N-ACETYLNEURAMINATE - GM(1) SIALYLTRANSFERASE (SAT-IV) ACTIVITY ON THE CERAMIDE COMPOSITION OF GM(1) GANGLIOSIDE, FEBS letters, 383(3), 1996, pp. 223-226
The dependence of CMP-N-acetylneuraminate:GM(1) sialyltransferase (SAT
IV) activity of rat liver Golgi apparatus on GM(1) ganglioside cerami
de composition was evaluated. SAT IV activity was assayed on GM(1) mol
ecular species carrying homogeneous ceramide moieties containing long
chain bases of different length (18 or 20 C atoms) unsaturated or not,
linked to 14:0, 16:0, 18:0 or 22:0 fatty acids. The results obtained
in the presence of the detergent Triton CF-54, when enzyme and substra
te are presumably part of the same supramolecular structure, show that
either the long chain base or the fatty acid composition can affect e
nzyme activity. This feature was not displayed when GM(1) was embedded
in dipalmitoylphosphatidylcholine vesicles in the absence of detergen
t. Under the latter conditions, the enzyme was not sensitive to the li
pid composition of GM(1) but to the ganglioside/phospholipid ratio in
the vesicles. These results indicate for the first time that SAT IV is
affected by the lipid composition of the substrate and strengthen the
hypothesis that glycosyltransferases may contribute to control the ce
llular glycosphingolipid ceramide pattern.