L-threo-Sphingosine C-18, an analog of D-erythro-sphingosine, inhibits PKC (protein kinase C) in mixed micelle assays with 50% inhibition at 2.2 mol % making it a slightly more stronger inhibitor compared to D-erythro-sphingosine (50% inhibition at 2.8 mol %) or other analogs of shorter alkyl chain length. Addition of L-threo-Sphingosine C-18 to primary cultured cerebellar cells does not decrease serine palmitoyltransferase (SPT) activity, the rate-limiting enzyme in ceramide biosynthesis, whereas under similar conditions D-erythro-sphingosine inhibits SPT activity. Sphingosines are long-chain base precursors of cellular sphingolipids and are used directly in the synthesis of ceramide. Sphingosine can exist in four stereoisomers, however only D-erythro-sphingosine occurs naturally.
