PROTEIN-SYNTHESIS IN SYNAPTOSOMAL FRACTIONS - ULTRASTRUCTURAL AUTORADIOGRAPHIC STUDY
PROTEIN-SYNTHESIS IN SYNAPTOSOMAL FRACTIONS - ULTRASTRUCTURAL AUTORADIOGRAPHIC STUDY
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DOI：
10.1083/jcb.52.3.526
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发表时间：
1972-01-01
影响因子：
7.8
通讯作者：
AUTILIOG.LA
中科院分区：
文献类型：
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作者：
GAMBETTI, P;GONATAS, NK;AUTILIOG.LA
在体外蛋白质合成的定量超微放射自显影研究已进行了大鼠突触体组分与氚化亮氨酸或氚化氨基酸混合物孵育。颗粒密度分布分析表明，突触前末梢被标记。30-50%的发育颗粒，代表掺入蛋白质的氚化氨基酸，与突触前末梢有关，占总突起的75-77 0/0。34- 45%的颗粒与含有核糖体的突起有关，而含有核糖体的突起仅占总突起的4-7%。这些含有核糖体的过程，其中一些可以被确定为突触后元件的相对比活性比突触前结束的高10倍。这些研究结果表明，蛋白质合成发生在体外突触前末梢，虽然在一个显着的程度低于发生在含核糖体的过程中，这与其他nonpresynaptic过程，在目前的时间是不可避免的污染物的突触体部分。标记了放射自显影中不含线粒体的突触前末梢。此外，突触前末梢标记孵育后的氯霉素抑制20%的突触体部分的蛋白质合成的存在下。结论：在离体条件下，突触前神经末梢除了线粒体蛋白质合成外，还存在另一个蛋白质合成系统。可能是PE本身蛋白质合成的结果，来自核周体的标记蛋白质的快速轴浆流的结果，或来自细胞外空间和邻近细胞结构的蛋白质摄取的结果。生物化学研究表明，标记的氨基酸通过突触体组分掺入蛋白质中（2-4），但是，在超微结构检查中，突触体组分除了PE外，还包括大量的非突触前突起（NP），其中一些含有核糖体（3）。由于以前的研究未能明确表明蛋白质合成发生在PE，目前的超微结构，
A quantitative ultrastructural radioautographic study of in vitro protein synthesis has been carried out in rat synaptosomal fractions incubated with tritiated leucine or a tritiated amino acid mixture. Analysis of grain density distribution demonstrated that presynaptic endings are labeled. 30-50% of the developed grains, representing tritiated amino acids incorporated into proteins, were related to presynaptic endings which accounted for 75-77 0/0 of the total processes. 34-45%% of the grains were related to processes containing ribosomes which accounted for only 4-7% of the total processes. The relative specific activity of these ribosome-containing processes, some of which could be identified as postsynaptic elements, was up to ten times higher than that of the presynaptic ending. These findings indicate that protein synthesis takes place in vitro in presynaptic terminals although to a significantly lesser degree than that occurring in ribosome-containing processes, which, with other nonpresynaptic processes, are at the present time unavoidable contaminants of synaptosomal fractions. Presynaptic endings that in radioautographs contained no mitochondria were labeled. Also, presynaptic endings were labeled after incubation in the presence of chloramphenical which inhibited 20% of the protein synthesis of the synaptosomal fraction. It is concluded that besides mitochondrial protein synthesis, another protein synthesizing system operates in presynaptic endings in vitro. be the result of protein synthesis in the PE itself, of fast axoplasmic flow of labeled proteins from the perikaryon, or of uptake of proteins from the extracellular space and adjacent cellular structures. Biochemical studies have shown incorporation of labeled amino acids into proteins by synaptosomal fractions (2-4), but, on ultrastructural examination, the synaptosomal fractions included, in addition to PE, a significant number of nonpresynaptic processes (NP), some of which contained ribosomes (3). Since previous investigations failed to show unequivocally that protein synthesis occurs at the PE, the present ultrastruc-