ブタ副腎ミクロソームのステロイド17α-ヒドロキシラーゼ-C_17,20リアーゼ(チトクロームP-450) : プロゲステロンによるリアーゼ活性の阻害と17α-ヒドロキシプロゲステロンによるヒドロキシラーゼ活性の阻害

抄録

Highly purified 17α-hydroxylase-C_{17, 20} lyase (cytochrome P-450) from porcine adrenocortical microsomes was incubated with [4-¹⁴C]-C₂₁-steroid substrate in the presence of cytochrome P-450 reductase and nicotinamide adenine dinucleotide phosphate as a cofactor. On the kinetic analysis, C_{17, 20} lyase activity was strongly inhibited by progesterone. The inhibition was competitive, and K₁ value for progesterone was 0.9μM. In addition, 17α-hydroxylase activity was inhibited by 17α-hydroxyprogesterone. The inhibition was competitive, and K₁ value for 17α-hydroxyprogesterone was 7.5μM. These results suggest that both hydroxylase and lyase reactions are catalyzed on a single active site.