The stimulatory role of human cytochrome b₅ in the bioactivation activities of human CYP1A2, 2A6 and 2E1: A new cell expression system to study cytochrome P450-mediated biotransformation (a corrigendum report on Duarte et al. (2005) Mutagenesis 20, 93-100)

This corrigendum report describes the study of the comparison of human cytochrome b₅ (b₅) with rat b₅ when coupled with human cytochrome P450 CYP1A2, 2A6 or 2E1. Results indicate a role of the N-terminal part of b₅ in the coupling with CYP. Indeed, the plasmid pLCM-b₅-RED used in our former study on b₅ [Duarte et al. (2005) Mutagenesis, 20(2), 193-100] erroneously contained rat b₅. Plasmid pLCM-b₅-RED was corrected with human b₅ and subsequently all experimental work was repeated as was described for the rat b₅ plasmid. Although absolute values of contents and activities were lower, all key-findings as found for rat b₅ could be confirmed using human b₅. The physiological relevant co-expression of the members of the cytochrome P450 complex, CYP, NADPH-cytochrome P450 oxidoreductase (RED) and human b₅ could be demonstrated in the different BTC strains, as was found before. The stimulatory effect of human b₅ on the activity of CYP1A2, CYP2A6 and CYP2E1 was in general similar, when compared with rat b ₅, though less quantitatively pronounced. This was both the case when using membrane preparations as well as by the bioactivation of procarcinogens using the bacterial mutagenicity assay. Human b₅ stimulated the bioactivation of all compounds as described for rat b₅, except for CYP1A2 mediated bioactivation of 2-aminoanthracene (2AA), which was not stimulated by human b₅. All other main findings of the effect of rat b₅ were confirmed with human b₅, i.e. for CYP2A6: N-nitrosodiethylamine (NNdEA): ∼14-fold increase (∼23-fold with rat b₅) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK): ∼3-fold (∼9-fold with rat b₅); for CYP2E1: NNdEA: ∼1.5-fold increase (∼3-fold with rat b₅); NNK: no mutagenicity with or without human b₅. Both CYP2A6 and CYP2E1 demonstrated total dependence on the presence of human b₅ for N-nitrosodi-n-propylamine (NNdPA) mutagenicity, as was shown before with rat b₅.