EC 1.14.14.176     
Accepted name: taxadiene 5α-hydroxylase
Reaction: taxa-4,11-diene + [reduced NADPH—hemoprotein reductase] + O2 = taxa-4(20),11-dien-5α-ol + [oxidized NADPH—hemoprotein reductase] + H2O
Systematic name: taxa-4,11-diene,[reduced NADPH—hemoprotein reductase]:oxygen oxidoreductase (5α-hydroxylating)
Comments: This microsomal cytochrome-P-450 (heme-thiolate) enzyme is involved in the biosynthesis of the diterpenoid antineoplastic drug taxol (paclitaxel). The reaction includes rearrangement of the 4(5)-double bond to a 4(20)-double bond, possibly through allylic oxidation.
References:
1.  Hefner, J., Rubenstein, S.M., Ketchum, R.E., Gibson, D.M., Williams, R.M. and Croteau, R. Cytochrome P450-catalyzed hydroxylation of taxa-4(5),11(12)-diene to taxa-4(20),11(12)-dien-5α-ol: the first oxygenation step in taxol biosynthesis. Chem. Biol. 3 (1996) 479–489. [PMID: 8807878]
[EC 1.14.14.176 created 2002 as 1.14.99.37, transferred 2020 to EC 1.14.14.176]