Preparation of Fluorescence-Labeled GM1 and Sphingomyelin by the Reverse Hydrolysis Reaction of Sphingolipid Ceramide N-Deacylase as Substrates for Assay of Sphingolipid-Degrading Enzymes and for Detection of Sphingolipid-Binding Proteins

Abstract

Sphingolipid ceramide N-deacylase is an enzyme capable of hydrolyzing the N-acyl linkages of ceramides of various sphingolipids. Recently, it was found that the enzyme catalyzes the reverse hydrolysis reaction in which free fatty acids are condensed to lyso-sphingolipids to produce sphingolipids. This paper describes a simple method for the synthesis of fluorescence-labeled sphingolipids utilizing the condensation reaction of the enzyme. N-TFAc-aminododecanoic acids were efficiently condensed by the enzyme to the lyso-forms of GM1 and sphingomyelin in glycine buffer (pH 10). The reaction products, N-TFAc-amino-GM1 and sphingomyelin, were obtained with overall yields of 60%. The purified products were identified to be ω-amino-GM1 and ω-amino-sphingomyelin, respec-tively, by TLC and FAB-MS or ESI-LC/MS analysis after removal of the N-TFAc by mild alkaline treatment. NBD-labeled GM1 and sphingomyelin were prepared from ω-amino-GM1 and ω-amino-sphingomyelin by coupling with 4-fluoro-NBD. These fluorescence-labeled substrates, C12-NBD-GMI and C12-NBD-sphingomyelin, were hydrolyzed by endoglycoceramidase and sphingomyelinase, respectively, to produce NBD-dodecanoyl-sphingosines, but were resistant to hydrolysis by sphingolipid ceramide N-deacylase. C12-NBD-sphingomyelin was found to be a better substrate than the commercially available C6-NBD-sphingomyelin for the assay of sphingomyelinase from various sources. We also describe a new method to detect GM1-binding proteins using fluorescence-labeled GM1.