Biochem/physiol Actions Fungal metabolite with potent immunosuppressant activity. Inhibits serine palmitoyltransferase at picomolar concentrations blocking synthesis of ceramide, a precursor of sphingomyelin and glycosphingolipids. Disrupts substratum adhesion of melanoma cells. It has been suggested that its immunosuppressant activity in the cytotoxic T-cell line CTTL-2 is due to apoptosis induction.