Dependence of rat liver CMP‐N‐acetylneuraminate:GM1 sialyltransferase (SAT IV) activity on the ceramide composition of GM1 ganglioside

摘要

>The dependence of CMP-N-acetylneuraminate:GM₁ sialyltransferase (SAT IV) activity of rat liver Golgi apparatus on GM₁ ganglioside ceramide composition was evaluated. SAT IV activity was assayed on GM₁ molecular 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 substrate are presumably part of the same supramolecular structure, show that either the long chain base or the fatty acid composition can affect enzyme activity. This feature was not displayed when GM₁ was embedded in dipalmitoylphosphatidylcholine vesicles in the absence of detergent. Under the latter conditions, the enzyme was not sensitive to the lipid composition of GM₁ 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 cellular glycosphingolipid ceramide pattern.