Acetylation of Sphingosine by PAF-Dependent Transacetylase

Abstract

Sphingosine induces many protein kinase C-dependent and -independent effects on biological systems. In parallel, C₂-ceramide used by investigators as an unnatural, cell permeable analog of long-chain acyl-ceramides, possesses biological activities similar with natural ceramides. We have recently characterized a membrane-associated, CoA-independent transacetylase that can transfer the acetate group from PAF to sphingosine and form C₂-ceramide. This enzyme has a strict stereochemical configuration requirement for sphingosine; only the naturally-occurring D-erythro-isomers of sphingosine accepts the acetate from PAF. Also, it has a rigid substrate specificity for sphingolipid-related analogues. Dipalmitoyl-glycerophosphocholine (-GPC) or hexadecylarachidonoyl-GPC can not transfer their long-chain acyl groups directly to sphingosine and sphingosine can not be acetylated by acetyl-CoA:lyso-PAF acetyltransferase. Results obtained from studies on pH optima, subcellular distribution, temperature sensitivities, inhibitors, tissue distributions, and expression of enzyme activities in Xenopus oocytes suggest that PAF:sphingosine transacetylase is similar, but not identical to the PAF:lysophospholipid transacetylase we have previously identified. The transacetylases function to diversify the biological responses of PAF.