RESUMEN
Free sphingosine, a material with multiple and potent biological activities, is known to occur in high concentration in mammalian epidermis. In the present study, thin-layer chromatography showed that in lipid extracts of human and pig stratum corneum, sphingosine forms a relatively stable compound with endogenous cholesteryl sulfate. NMR spectrometry of sphingosine and its hydrochloride, sulfate, and mixtures with cholesteryl or dodecyl sulfate showed that interaction with the organic sulfates constituted simple salt formation. Under neutral or weakly acidic conditions, such salts were only slightly dissociated and migrated on thin-layer chromatograms as discrete compounds. Thin-layer chromatography revealed undissociated salt formation between several long-chain bases and organic sulfates, and showed that their interaction is stoichiometric. However, undissociated salts were not formed between long-chain bases and fatty acids or phosphatidic acid. Undissociated salt formation may therefore be specific for organic bases and sulfates. It was concluded that the free sphingosine in the stratum corneum may be present as its cholesteryl sulfate salt and in this form be unavailable for permeation into the viable epidermal cells.
