Guzelian P S, Bissell D M
J Biol Chem. 1976 Jul 25;251(14):4421-7.
Synthesis of heme and cytochrome P-450 have been studied in adult rat hepatocytes in primary monolayer culture. Incubation of cells with delta-aminolevulinic acid increases both cellular heme and cytochrome P-450 relative to that found in cells incubated under control conditions. Formation of heme is proportional to the concentration of delta-aminolevulinic acid in the culture medium and is not saturable. By contrast, formation of cytochrome P-450 is saturable; excess intracellular heme appears as a new absorption band at 420 nm in the carbon monoxide-reduced difference spectrum. We have studied the effect of cobalt on heme and hemoprotein formation in this cell system. The metal blocks formation of cytochrome P-450 but fails to affect heme synthesis. In contrast to previous findings with isolated mitochondria, no cobalt protoporphyrin formed in hepatocytes cultured in the presence of the metal. In studies of rats in vivo, it was confirmed that cobalt acts to reduce the amount of [14C]heme in the liver after administration of delta-amino[14C]levulinic acid. However, the present findings suggest that this effect of cobalt represents accelerated breakdown of newly labeled hepatic heme rather than inhibition of synthesis. We conclude that cobalt interferes with formation of cytochrome P-450 not by direct inhibition of heme synthesis but most likely by blocking the association of heme and apocytochrome.
已在原代单层培养的成年大鼠肝细胞中研究了血红素和细胞色素P - 450的合成。与在对照条件下培养的细胞相比，用δ-氨基乙酰丙酸孵育细胞可增加细胞内血红素和细胞色素P - 450的含量。血红素的形成与培养基中δ-氨基乙酰丙酸的浓度成正比，且不饱和。相比之下，细胞色素P - 450的形成是可饱和的；过量的细胞内血红素在一氧化碳还原差光谱中在420nm处呈现为新的吸收带。我们研究了钴对该细胞系统中血红素和血红蛋白形成的影响。这种金属可阻断细胞色素P - 450的形成，但不影响血红素的合成。与先前对分离线粒体的研究结果不同，在有该金属存在的情况下培养的肝细胞中未形成钴原卟啉。在对大鼠的体内研究中，证实了钴在给予δ-氨基[14C]乙酰丙酸后可降低肝脏中[14C]血红素的含量。然而，目前的研究结果表明，钴的这种作用代表新标记的肝脏血红素加速分解，而非合成抑制。我们得出结论，钴干扰细胞色素P - 450的形成不是通过直接抑制血红素合成，而是很可能通过阻断血红素与脱辅基细胞色素的结合。
