Functional characterization of CYP3A4.16: Catalytic activities toward midazolam and carbamazepine

K. Maekawa, T. Yoshimura, Y. Saito, Y. Fujimura, F. Aohara, C. Emoto, K. Iwasaki, N. Hanioka, S. Narimatsu, T. Niwa, J. Sawada

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)


1. To assess the substrate-dependent effects of the low-activity allele of human CYP3A4, CYP3A4*16 (Thr185Ser), a recombinant wild-type (CYP3A4.1) or variant (CYP3A4.16) protein was co-expressed with human NADPH-P450 reductase in Sf21 insect cells using a baculovirus-insect cell system. 2. The holo-CYP3A4 protein level of CYP3A4.16 in insect microsomes was slightly higher than that of CYP3A4.1, while no difference in total (apo- and holo-) CYP3A4 protein levels was observed between them. 3. When midazolam was used as a substrate, Km and Vmax for 1'-hydroxylation in CYP3A4.16 were significantly higher and lower, respectively, than those in the wild-type, resulting in a 50% decrease in intrinsic clearance (Vmax/Km) of the variant. In contrast, intrinsic clearance for 4-hydroxylation of the variant was decreased by 30% due to a significant increase in Km without a difference in Vmax. 4. Both the wild-type and variant exhibited sigmoidal kinetic profiles for carbamazepine 10,11-epoxide formation. When the modified two-site equation was applied for the analysis of kinetic parameters, Km2 and Vmax2 of CYP3A4.16 were approximately two times higher and lower than those of the wild-type, resulting in a 74% decrease in intrinsic clearance. 5. These results demonstrated that CYP3A4.16 shows the substrate-dependent altered kinetics compared with CYP3A4.1.

Original languageEnglish
Pages (from-to)140-147
Number of pages8
Issue number2
Publication statusPublished - Feb 2009
Externally publishedYes


  • CYP3A4
  • Function
  • Non-synonymous single nucleotide polymorphism (SNP)
  • Substrate dependency

ASJC Scopus subject areas

  • Biochemistry
  • Toxicology
  • Pharmacology
  • Health, Toxicology and Mutagenesis


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