Theoretical calculation of triazolam hydroxylation and endogenous steroid inhibition in the active site of CYP3A4

Nao Torimoto, Itsuko Ishii, Masayuki Hata, Yukari Kobayashi, Hiroyoshi Nakamura, Noritaka Ariyoshi, Mitsukazu Kitada

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CYP3A4 has unusual kinetic characteristics because it has a large active site. CYP3A4 produced more 4-hydroxytriazolam than α-hydroxytriazolam at concentrations of more than 60 μM triazolam, and different steroids had different inhibitory effects on the system. To clarify these interesting observations, the interactions between substrate and substrate/steroid were investigated by theoretical calculations. When two triazolam molecules were docked into the active site, the distance between the O-atom and the 4-hydroxylated site was less than the distance to the α-hydroxylated site because of interaction between the two triazolam molecules. Estradiol inhibited both α- and 4-hydroxytriazolam formation by 50%. Dehydroepiandrosterone (DHEA) inhibited α-hydroxylation more than 4-hydroxytriazolam formation, whereas aldosterone had no effect. When one triazolam molecule and one steroid molecule were simultaneously docked, estradiol increased the distance between the O-atom and the two hydroxylated sites, DHEA only increased the distance between the O-atom and α-hydroxylated site, and aldosterone did not change the distances. The relevant angles of Fe-O-C in the hydroxylated site of triazolam also widened, together with increased distance. These findings indicate that formation of a substrate and substrate/effector complex in the active site may be a factor for determining the enzyme kinetic parameters of CYP3A4.

Original languageEnglish
Pages (from-to)223-232
Number of pages10
JournalBiochimica et Biophysica Acta - Proteins and Proteomics
Issue number2
Publication statusPublished - Feb 2007
Externally publishedYes



  • CYP3A4
  • Endogenous steroid
  • Theoretical calculation
  • Triazolam

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Genetics

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