3-Ketosphingolipids: application to the determination of sphingolipids which contain 4-sphingenine.

1. Ceramides and cerebrosides, both with 2-hydroxy or non-hydroxy fatty acids, and sphingomyelins were converted quantitatively to the corresponding 3-keto derivatives with the oxidative reagent 2,3-dichloro-5,6-dicyanobenzoquinone. Sulfatides were converted to 3-ketocerebrosides. 2. The conversion of these sphingolipids to the alpha,beta-unsaturated ketone permits three methods of quantitation: in Method I, the absorption of the reaction product is measured at 230 nm; Method II utilizes high performance liquid chromatography and an ultraviolet light detector; in Method III, the product is reduced with NaB3H4 and the radioactivity of the reduced products is determined. All three methods can be used to measure sphingolipids in nanomole quantities. 3. Methods I and II have been applied to the determination of cerebroside and sulfatide content of normal and metachromatic leukodystrophy brains. In the white matter of the pathological brains, there was a greater accumulation of sulfatides containing non-hydroxy fatty acids than of those containing 2-hydroxy fatty acids. The ceramide levels of the cerebellum in a Farber's disease patient and a control were determined by Method II. Method III was used to determine the content of free ceramides in human sera.