IUBMB Enzyme Nomenclature


Accepted name: steroid Δ-isomerase

Reaction: A 3-oxo-Δ5-steroid = a 3-oxo-Δ4-steroid

For diagram click here.

Other name(s): hydroxysteroid isomerase; steroid isomerase; Δ5-ketosteroid isomerase; Δ5(or Δ4)-3-keto steroid isomerase; Δ5-steroid isomerase; 3-oxosteroid isomerase; Δ5-3-keto steroid isomerase; Δ5-3-oxosteroid isomerase

Systematic name: 3-oxosteroid Δ54-isomerase

Comments: This activity is catalysed by several distinct enzymes (cf. EC, cholesterol oxidase and EC, 3-hydroxy-5-steroid dehydrogenase).

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number: 9031-36-1


1. Ewald, W., Werbein, H. and Chaikoff, I.L. Evidence for the presence of 17-hydroxypregnenedione isomerase in beef adrenal cortex. Biochim. Biophys. Acta 111 (1965) 306-312. [PMID: 5867327]

2. Kawahara, F.S. and Talalay, P. Crystalline Δ5-3-ketosteroid isomerase. J. Biol. Chem. 235 (1960) PC1-PC2.

3. Talalay, P. and Wang, V.S. Enzymic isomerization of Δ5-3-ketosteroids. Biochim. Biophys. Acta 18 (1955) 300-301.

[EC created 1961]

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