Intracellular localization of aspartate kinase and the enzymes of threonine and methionine biosynthesis in green leaves.
Intracellular localization of aspartate kinase and the enzymes of threonine and methionine biosynthesis in green leaves.
复制标题
绿叶中天冬氨酸激酶以及苏氨酸和蛋氨酸生物合成酶的细胞内定位。
作者：
R. Wallsgrove;P. Lea;B. Miflin
研究了豌豆（Pisumsativumcv费尔瑟姆First）和大麦（Hordeumvulgarecv Julia）叶片中几种天冬氨酸途径酶的细胞内定位。原生质体裂解物通过差速或蔗糖密度梯度离心在针对每种酶优化的培养基中分级。结果表明，天冬氨酸激酶、高丝氨酸激酶、苏氨酸合成酶和胱硫醚γ-合成酶仅限于叶绿体。胱硫醚β-裂合酶似乎存在于几个馏分中，但总活性的50%以上与叶绿体有关。与此相反，无论是甲硫氨酸合酶，也没有甲硫氨酸腺苷转移酶显着与叶绿体，只有一小部分的甲硫氨酸合酶与线粒体组分。甲硫氨酸腺苷转移酶，因此S-腺苷甲硫氨酸合成，是没有发现在任何细胞器部分。结论是，苏氨酸和赖氨酸一样，只在叶绿体中合成，而蛋氨酸生物合成的最后一步主要发生在细胞质中。
The intracellular localization of several aspartate pathway enzymes has been studied in pea (Pisum sativum cv Feltham First) and barley (Hordeum vulgare cv Julia) leaves. Protoplast lysates were fractionated by differential or sucrose density gradient centrifugation, in media optimized for each enzyme. The results show that aspartate kinase, homoserine kinase, threonine synthase, and cystathionine gamma-synthase are confined to the chloroplast. Cystathionine beta-lyase appears to be present in several fractions, though more than 50% of the total activity is associated with the chloroplasts. In contrast, neither methionine synthase nor methionine adenosyl-transferase were significantly associated with chloroplasts, and only a small proportion of the methionine synthase was associated with the mitochondrial fraction. Methionine adenosyltransferase, and hence S-adenosylmethionine synthesis, is not found in any organelle fraction. The conclusion is that whereas threonine, like lysine, is synthesized only in the chloroplast, the last step in methionine biosynthesis occurs largely in the cytoplasm.