Skip to main content
PMC home page
Biochemical Journal logoLink to Biochemical Journal
. 1980 Feb 1;185(2):411–421. doi: 10.1042/bj1850411

Mechanistic and stereochemical studies on 3-oxo steroid delta 4-delta 5-isomerase from human placenta.

M Akhtar, M Calder, T Smith, J N Wright
PMCID: PMC1161368  PMID: 7396823

Abstract

The mechanism of isomerization of delta 5-3-ox steroids to delta 4-3-oxo steroids was examined by using the membrane-bound 3-oxo steroid delta 4-delta 5-isomerase (EC 5.3.3.1) and the 3 beta-hydroxy steroid dehydrogenase present in the microsomal fraction obtained from full-term human placenta. (1) Methods for the preparation of androst-5-ene-3 beta, 17 beta-diol specifically labelled at the 4 alpha-, 4 beta- or 6-positions are described. (2) Incubations with androst-5-ene-3 beta, 17 beta-diol stereospecifically 3H-labelled either in the 4 alpha- or 4 beta-position showed that the isomerization reaction occurs via a stereospecific elimination of the 4 beta hydrogen atom. In addition, the complete retention of 3H in the delta 4-3-oxo steroids obtained from [4 alpha-3H]androst-5-ene-3 beta, 17 beta-diol indicates that the non-enzymic contribution to these experiments was negligible. (3) To study the stereochemistry of the insertion of the incoming proton at C-6, the [6-3H]androst-4-ene-3, 17-dione obtained from the oxidation isomerization of [6-3H]androst-5-ene-3 beta, 17 beta-diol was enzymically hydroxylated in the 6 beta-position by the fungus Rhizopls stolonifer. Retention of 3H in the 6 alpha-position of the isolated 6 beta-hydroxyandrost-4-ene-3, 17-dione indicates that in the isomerase-catalysed migration of the C(5) = C(6) double bond, the incoming proton from the acidic group on the enzyme must enter C-6 from the beta-face, forcing the existing 3H into the 6 alpha-position.

Full text

PDF
412

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Achmatowicz S., Barton D. H., Magnus P. D., Poulton G. A., West P. J. Photochemical transformations. XXX. Photolysis of thiobenzoic acid O-esters. I. Photolysis of O-cholesteryl thiobenzoate. J Chem Soc Perkin 1. 1973;15:1567–1570. doi: 10.1039/p19730001567. [DOI] [PubMed] [Google Scholar]
  2. Akhtar M., Skinner S. J. The intermediary role of a 19-oxoandrogen in the biosynthesis of oestrogen. Biochem J. 1968 Sep;109(2):318–321. doi: 10.1042/bj1090318. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. RYAN K. J. Biological aromatization of steroids. J Biol Chem. 1959 Feb;234(2):268–272. [PubMed] [Google Scholar]
  4. Rose I. A. Mechanism of the aldose-ketose isomerase reactions. Adv Enzymol Relat Areas Mol Biol. 1975;43:491–517. doi: 10.1002/9780470122884.ch6. [DOI] [PubMed] [Google Scholar]
  5. Smith A. G., Brooks C. J. The substrate specificity and stereochemistry, reversibility and inhibition of the 3-oxo steroid delta 4-delta 5-isomerase component of cholesterol oxidase. Biochem J. 1977 Oct 1;167(1):121–129. doi: 10.1042/bj1670121. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. TALALAY P., DOBSON M. M., TAPLEY D. F. Oxidative degradation of testosterone by adaptive enzymes. Nature. 1952 Oct 11;170(4328):620–621. doi: 10.1038/170620a0. [DOI] [PubMed] [Google Scholar]
  7. TALALAY P., WANG V. S. Enzymic isomerization of delta5-3-ketosteroids. Biochim Biophys Acta. 1955 Oct;18(2):300–301. doi: 10.1016/0006-3002(55)90079-2. [DOI] [PubMed] [Google Scholar]

Articles from Biochemical Journal are provided here courtesy of The Biochemical Society

RESOURCES