New Control Mechanism for Protein Transport in Cells

线粒体膜外膜细胞色素b(OMB)是在大鼠肝脏中发现的一种微粒体细胞色素b_5(B_5)的同系物。在间质细胞中，OMB与催化雄激素生成的细胞色素P-450lt；17α&gt；共定位，而b5未被检测到。我们已经证明，在有限但生理的P-450还原酶的作用下，OMB能刺激P-45O和17α&gt；的17α羟基酶和裂解酶反应，从而促进孕酮产生雄烯二酮。因此，OMband Not b_5被认为是大鼠睾丸雄激素发生的调节器，被认为是负责激活的基因。这一发现促使我们研究OMB的新的生理功能。我们用免疫组织化学方法分析了OMB、b_5和P-45O_(？)17α&gt；在大鼠体内的组织定位。在肾上腺皮质，OMB和B5分别主要分布在外侧和内侧。在小脑中，OMB和P-450lt；17α&gt；仅在神经类固醇生成的主要部位浦肯野细胞中检测到并共定位。在大脑中，它们共同分布在脉络丛的室管膜细胞中，脉络丛产生脑脊液。OMB也存在于海马区和神经节层。相反，在大脑中几乎没有观察到b5。部分纯化的蒲肯野细胞从孕酮中产生睾酮，表明P-450和17-α&gt；和17-β-羟基类固醇脱氢酶在转化过程中都是活跃的，这表明OMB可能负责刺激细胞中P-450和17-α&gt；这些结果表明，OMB不仅在普通内分泌系统中具有重要功能，而且在高等生命活动中也具有重要作用。

Outer mitochondrial membrane cytochrome b (OMb) was discovered in rat liver as a homologue of microsomal cytochrome b_5 (b_5). OMb was co-localized in Leydig cells with cytochrome P-450_<17α>, which catalyzes androgengenesis therein, whereas b_5 was undetectable. We have demonstrated that OMb stimulates the 17α-hydroxylase and lyase reactions of P-45O_<17α> under limited but physiological amounts of P-450 reductase, leading to an enhanced production of androstenedione from progesterone. Thus, OMband not b_5, which was believed to be responsible for the activation, was identified as a modulator for androgengenesis in rat testes. This finding prompted us to study the novel physiological functions of OMb. We analyzed the tissue localization of OMb, b_5 and P-45O_<17α> in rats by immunohistochemical staining. In the adrenal cortex OMb and b_5 were mainly present in the outer and inner portions, respectively. In the cerebellum OMb and P-450_<17α> were only detected and co-localized in the Purkinje cell, a major site for neurosteroidogenesis. In cerebrum they were co-localized in the ependymal cells of choroid plexus, which produces the cerebrospinal fluid. OMb was present also in the hippocampus and ganglionic layer. In contrast, b_5 was scarcely observed in the brain. Partially purified Purkinje cells produced testosterone from progesterone, indicating that both P-450_<17α> and 17β-hydroxysteroid dehydrogenase were active in the conversion and suggested that OMb could be responsible for stimulation of P-450_<17α>-catalyzed reactions in the cells. These results imply important functions of OMb in not only ordinary endocrine systems but also in higher life activities.