title: Structure determination of soybean and wheat glucosylceramides by tandem mass spectrometry.
abstract: Glucosylceramide (GluCer) is a major sphingolipid of plant tissue and, thus, abundant in nature and in dietary food sources. The lipid backbones of mammalian GluCer (sphingosine, d18:1(delta4), and ceramide) induce cell death (apoptosis) and inhibit colon carcinogenesis, it is critical to know the structures of GluCer present in plants as a first step toward understanding this potential link between diet and cancer. This study characterized the molecular species of GluCer from soybean and wheat by low-resolution, high-resolution and tandem mass spectrometry. Soybean GluCer was comprised primarily (>95%) of ceramide with 4,8-sphingadiene (d18:2(delta4,delta8)) and alpha-hydroxypalmitic acid (h16:0); the remainder had the same backbone with h18:0, h20:0, h22:0 and h24:0 fatty acids. Wheat GluCer had three major ceramide, d18:2(delta4,delta8) with h16:0, d18:1(delta8) with h16:0 and d18: 2(delta4,delta8) with h20:0, and smaller amounts of other homologs. These backbones differ from those of mammalian sphingolipids, which often have a delta4-double bond (but rarely a delta8-double bond), and have alpha-hydroxy fatty acids in only some cases. Previously unexplained fragmentations that were diagnostic for the type of sphingoid base backbone (i.e. by homolytic cleavage of the doubly allylic C-6-C-7 bond to yield a stable distonic allylic radical cation and an allylic radical neutral) were also identified. Hence this method should be useful in the identification of double bonds in sphingolipids, and structure-function relationships between sphingolipids and colon carcinogenesis.
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322-3050, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Sullards
authors.forename: D V
authors.initials: DV
authors.lastname: Lynch
authors.forename: A H
authors.initials: AH
authors.lastname: Merrill
authors.forename: J
authors.initials: J
authors.lastname: Adams
mesh_terms: D005963:Glucosylceramides / Q000737:chemistry*; D015394:Molecular Structure; D013025:Glycine max / Q000737:chemistry; D016339:Spectrometry, Mass, Fast Atom Bombardment / Q000379:methods*; D014908:Triticum / Q000737:chemistry
chemical_list: D005963:Glucosylceramides