DEGS1 (sphingolipid delta(4)-desaturase 1 / “degenerative spermatocyte homolog 1”) enzyme associated with the cytosolic face of the endoplasmic reticulum catalyzes the desaturation of dihydroceramide to form ceramide (Cadena et al. 1997; Ternes et al. 2002). The stoichiometry and cofactor requirements of the reaction are inferred from those observed in studies of ceramide synthesis in vitro catalyzed by rat liver microsomes (Michel et al. 1997). DEGS1 may also catalyze the 4-hydroxylation of dihydroceramide to form 4-hydroxysphinganine, but with low efficiency.