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). {ECO:0000250|UniProtKB:Q5F3C1, ECO:0000269|PubMed:11937514, ECO:0000269|PubMed:30620337, ECO:0000269|PubMed:30620338}. This is the function of ENSG00000143753 (DEGS1, delta 4-desaturase, sphingolipid 1).