||The enzyme, which has been characterized from plants, fungi, and mammals, generates a trans double bond at position 4 of sphinganine bases in sphingolipids . The preferred substrate is dihydroceramide, but the enzyme is also active with dihydroglucosylceramide . Unlike EC 126.96.36.199, sphingolipid 8-desaturase, this enzyme does not contain an integral cytochrome b5 domain  and requires an external cytochrome b5 . The product serves as an important signalling molecules in mammals and is required for spermatide differentiation .
||Stoffel, W., Assmann, G. and Bister, K. Metabolism of sphingosine bases. XVII. Stereospecificities in the introduction of the 4t-double bond into sphinganine yielding 4t-sphingenine (sphingosine). Hoppe-Seylers Z. Physiol. Chem. 352 (1971) 1531–1544. [PMID: 5140816]
||Michel, C., van Echten-Deckert, G., Rother, J., Sandhoff, K., Wang, E. and Merrill, A.H., Jr. Characterization of ceramide synthesis. A dihydroceramide desaturase introduces the 4,5-trans-double bond of sphingosine at the level of dihydroceramide. J. Biol. Chem. 272 (1997) 22432–22437. [DOI] [PMID: 9312549]
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||Michaelson, L.V., Zäuner, S., Markham, J.E., Haslam, R.P., Desikan, R., Mugford, S., Albrecht, S., Warnecke, D., Sperling, P., Heinz, E. and Napier, J.A. Functional characterization of a higher plant sphingolipid Δ4-desaturase: defining the role of sphingosine and sphingosine-1-phosphate in Arabidopsis. Plant Physiol. 149 (2009) 487–498. [DOI] [PMID: 18978071]