Palmer A, Rivett A J, Thomson S, Hendil K B, Butcher G W, Fuertes G, Knecht E
Instituto de Investigaciones Citológicas, Valencia, Spain.
Biochem J. 1996 Jun 1;316 ( Pt 2)(Pt 2):401-7. doi: 10.1042/bj3160401.
Mammalian proteasomes are composed of 14-17 different types of subunits, some of which, including major-histocompatibility-complex-encoded subunits LMP2 and LMP7, are non-essential and present in variable amounts. We have investigated the distribution of total proteasomes and some individual subunits in rat liver by quantitative immunoblot analysis of purified subcellular fractions (nuclei, mitochondria, microsomes and cytosol). Proteasomes were mainly found in the cytosol but were also present in the purified nuclear and microsomal fractions. In the nuclei, proteasomes were soluble or loosely attached to the chromatin, since they could be easily extracted by treatment with nucleases or high concentrations of salt. In the microsomes, proteasomes were on the outside of the membranes. Further subfractionation of the microsomes showed that the proteasomes in this fraction were associated with the smooth endoplasmic reticulum and with the cis-Golgi but were practically absent from the rough endoplasmic reticulum. Using monospecific antibodies for some proteasomal subunits (C8, C9, LMP2 and Z), the composition of proteasomes in nuclei, microsomes and cytosol was investigated. Although there appear not to be differences in proteasome composition in the alpha subunits (C8 and C9) in the different locations, the relative amounts of some beta subunits varied. Subunit Z was enriched in nuclear proteasomes but low in microsome-associated proteasomes, whereas LMP2, which was relatively low in nuclei, showed a small enrichment in the microsomes. These differences in subunit composition of proteasomes probably reflect differences in the function of proteasomes in distinct cell compartments.
哺乳动物蛋白酶体由14 - 17种不同类型的亚基组成，其中一些亚基，包括主要组织相容性复合体编码的亚基LMP2和LMP7，并非必需，且含量可变。我们通过对纯化的亚细胞组分（细胞核、线粒体、微粒体和细胞质）进行定量免疫印迹分析，研究了大鼠肝脏中总蛋白酶体和一些单个亚基的分布。蛋白酶体主要存在于细胞质中，但也存在于纯化的细胞核和微粒体组分中。在细胞核中，蛋白酶体是可溶的或松散地附着于染色质，因为用核酸酶或高浓度盐处理后它们很容易被提取出来。在微粒体中，蛋白酶体位于膜的外侧。对微粒体的进一步分级分离表明，该组分中的蛋白酶体与滑面内质网和顺式高尔基体相关，但在粗面内质网中几乎不存在。使用针对一些蛋白酶体亚基（C8、C9、LMP2和Z）的单特异性抗体，研究了细胞核、微粒体和细胞质中蛋白酶体的组成。尽管不同位置的α亚基（C8和C9）在蛋白酶体组成上似乎没有差异，但一些β亚基的相对含量有所不同。亚基Z在核蛋白酶体中富集，但在与微粒体相关的蛋白酶体中含量较低，而在细胞核中相对较低的LMP2在微粒体中略有富集。蛋白酶体亚基组成的这些差异可能反映了蛋白酶体在不同细胞区室中的功能差异。
