Tissue specificity of mitochondrial enzyme of higher plants.

我们研究了细胞色素c氧化酶的组织特异性，它是线粒体呼吸链的一个重要组成部分。该酶由线粒体dna编码亚基和核dna编码亚基组成。高等植物的组织可分为地上部和地下部，它们在不同的温度条件下生长。热带和亚热带作物的叶和茎组织暴露在极高的温度下，而根则在相对温和的温度下保持活力。叶片和茎组织的细胞色素c氧化酶对热失活的抗性强于根组织的细胞色素c氧化酶。这是由于酶分子的不同，而不是由于膜脂种类的不同。因为，从绿豆幼苗的下胚轴（地上组织）纯化的细胞色素c氧化酶比从根部纯化的酶更能抵抗热失活。然后，我们分析了细胞色素c氧化酶分子形态的变化。线粒体制造的亚基（I，II和Iv）的结构非常保守，这表明不存在亚基的组织特异性亚型。绿豆下胚轴细胞色素c氧化酶的核dna编码亚基（亚基VC）在免疫上与根不同。结果表明，至少在绿豆中，细胞色素c氧化酶的核编码亚基是组织特异性合成的。以甘薯为例，根组织和茎组织中同一酶复合体中Vc亚基的数量存在差异。我们认为细胞色素c氧化酶分子形态的变化可能导致酶热不稳定性的差异。

We have investigated the tissue specificity of cytochrome c oxidase which is an important element of the respiratory chain of mitochondria. The enzyme consists of the mitochondrial-DNA encoded and nuclear-DNA encoded subunits. The tissues of higher plants can be divided into the above- and below-ground parts and they grow in the different condition of temperature. The leaf and stem tissues of tropical and subtropical crops are exposed to an extremely high temperature, while roots are kept alive at a comparatively moderate temperature. Cytochrome c oxidases of the leaf and stem tissues were resistant to heat inactivation than the enzyme of the root tissue. This is due to the difference in the enzyme molecules rather than to the difference in membrane lipids species. Because, cytochrome c oxidase purified from the hypocotyl (above-ground tissue) of mung bean seedlings was more resistant to inactivation by heat than the enzyme from the root.Then, we have analyzed the variation in the molecular form of cytochrome c oxidase. The structure of mitochondrially made subunits (I,II and Iv) are very conservative, which suggests no existence of the tissue-specific isoform of the subunits. While a nuclear-DNA encoded subunit (subunit VC) of cytochrome c oxidase in mung bean hypocotyls differed immunologically from that in the roots. The result suggests that at least in mung bean, a nuclear-encoded subunit of cytochrome c oxidase is synthesized tissue-specifically. In the case of sweet potato, there was difference in the number of the subunit Vc in one enzyme complex between the enzymes from root and shoot tissues. We thought that the variation of the molecular form of cytochrome c oxidase may cause the difference in thermostagility of the enzyme.