Has sphingolipid-delta-4-desaturase activity. Converts D-erythro-sphinganine to D-erythro-sphingosine (E-sphing-4-enine) (PubMed:11937514, PubMed:30620337, PubMed:30620338). Catalyzes the equilibrium isomerization of retinols (By similarity). an N-acylsphinganine + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = an N-acylsphing-4-enine + 2 Fe(III)-[cytochrome b5] + 2 H2O all-trans-retinol = 11-cis-retinol all-trans-retinol = 9-cis-retinol all-trans-retinol = 13-cis-retinol 11-cis-retinol = 13-cis-retinol 11-cis-retinol = 9-cis-retinol Interacts with RLBP1; the interaction increases synthesis of chromophore-precursors by DEGS1. Ubiquitous. Myristoylation can target the enzyme to the mitochondria leading to an increase in ceramide levels. The disease is caused by variants affecting the gene represented in this entry. Belongs to the fatty acid desaturase type 1 family. DEGS subfamily.