Brands R, Hoogenraad N
Aust J Exp Biol Med Sci. 1986 Apr;64 ( Pt 2):165-73. doi: 10.1038/icb.1986.18.
We investigated the distribution of the nuclear encoded mitochondrial enzymes, carbamylphosphate synthetase (CPS; EC 6.3.4.16) and ornithine transcarbamylase (OTC; EC 2.1.3.3) in liver by immunocytochemistry on ultrathin sections using the protein A-gold technique. Both enzymes were found to be present as aggregates in the cytoplasm of hepatocytes, in association with ER membranes adjacent to mitochondria. Clusters of the enzymes were also found inside the mitochondria. The aggregation of these enzymes was found only with antibodies to CPS and OTC and not with antibodies against albumin or with IgG from unimmunized serum, nor were aggregates found in cells other than hepatocytes. The results are suggestive of localized uptake of clusters of enzyme or co-translational uptake of enzyme at discrete localizations and that endoplasmic reticulum (ER) associations may be necessary for uptake of the percursor forms of CPS and OTC. The possible involvement is discussed of micropinosomes which are seen associated with inner membrane, intermembrane space and outer membrane in mitochondria obtained from a perinuclear pellet where ER and mitochondria are frequently found in close association.
我们采用蛋白A-金技术，通过对超薄切片进行免疫细胞化学研究，调查了肝脏中核编码的线粒体酶——氨甲酰磷酸合成酶（CPS；EC 6.3.4.16）和鸟氨酸转氨甲酰酶（OTC；EC 2.1.3.3）的分布情况。发现这两种酶均以聚集体形式存在于肝细胞的细胞质中，与线粒体附近的内质网（ER）膜相关联。在线粒体内也发现了酶的簇集。仅用抗CPS和抗OTC抗体能发现这些酶的聚集，而用抗白蛋白抗体或未免疫血清的IgG则不能发现聚集，并且在肝细胞以外的细胞中也未发现聚集体。结果提示酶簇的局部摄取或酶在离散定位处的共翻译摄取，并且内质网（ER）关联对于CPS和OTC前体形式的摄取可能是必要的。本文讨论了微胞饮小体的可能参与情况，在从核周沉淀获得的线粒体中，微胞饮小体可见与线粒体内膜、膜间隙和外膜相关联，而在该沉淀中内质网和线粒体经常紧密相连。
