SPHK1 and multiple sclerosis: Conversely, d-erythro-sphingosine was the best substrate for SK1.230 Neither SK1 nor SK2 phosphorylates ceramides but a specific ceramide kinase has been discovered238 and cloned.239,240 SK1 has also been reported to accept GTP as a nucleotide substrate as well as ATP, albeit with a significantly reduced preference241 The immunosuppressive drug FTY720 (Fingolimod, GilenyaTM, see below) sold by Novartis to treat multiple sclerosis is, in fact a “pro-drug” that is phosphorylated by SK1 and SK2.233,242,243