Seven of the 57 human cytochrome P450 (P450) enzymes are mitochondrial and carry out important reactions with steroids and vitamins A and D. These seven P450s utilize an electron transport chain that includes NADPH, NADPH-adrenodoxin reductase (AdR), and adrenodoxin (Adx) instead of the diflavin NADPH-P450 reductase (POR) used by the other P450s in the endoplasmic reticulum. Although numerous studies have been published involving mitochondrial P450 systems, the experimental conditions vary considerably. We compared human Adx and bovine Adx, a commonly used component, and found very similar catalytic activities in reactions catalyzed by human P450s 11B2, 27A1, and 27C1. Binding constants of 6–200 nM were estimated for Adx binding to these P450s using microscale thermophoresis. All P450 catalytic reactions were saturated at 10 μM Adx, and higher concentrations were not inhibitory up to at least 50 μM. Collectively these studies demonstrate the tight binding of Adx (both human and bovine) to AdR and to several mitochondrial P450s and provide guidance for optimization of Adx-dependent P450 reactions.

57种人类细胞色素P450（P450）酶中有7种是线粒体，与类固醇，维生素A和D发生重要反应。这7种P450利用电子传输链，包括NADPH，NADPH-肾上腺素还原酶（AdR）和肾上腺素（Adx ），而不是内质网中其他P450使用的双黄素NADPH-P450还原酶（POR）。尽管已经发表了许多有关线粒体P450系统的研究，但实验条件却相差很大。我们比较了人类Adx和牛Adx（一种常用成分），发现在人类P450 11B2、27A1和27C1催化的反应中具有非常相似的催化活性。使用微尺度热泳估计Adx与这些P450的结合常数为6–200 nM。所有P450催化反应均在10μMAdx处饱和，至少50μM时，更高的浓度没有抑制作用。这些研究共同证明了Adx（人类和牛）与AdR和几种线粒体P450紧密结合，并为优化Adx依赖性P450反应提供了指导。