Konishi T, Sasaki Y
Department of Food Science and Technology, Faculty of Agriculture, Kyoto University, Japan.
Proc Natl Acad Sci U S A. 1994 Apr 26;91(9):3598-601. doi: 10.1073/pnas.91.9.3598.
Acetyl-CoA carboxylase (ACCase, EC 6.4.1.2) catalyzes the synthesis of malonyl-CoA, the first intermediate in fatty acid synthesis. We studied the localization of two forms, the prokaryote and the eukaryote forms, of ACCase in pea leaves by comparing the biotin polypeptides of the two ACCases in protein extract from leaves and plastids. We found that the two forms of ACCase were in different cell compartments of pea leaves; the prokaryote form was in the plastids, and the eukaryote form was elsewhere, probably in the cytosol. This result suggested the existence of two sites of malonyl-CoA synthesis. The Gramineae, such as rice and wheat, which lack the accD gene encoding one of the subunits of the prokaryote form of ACCase in their chloroplast genomes, did not have the prokaryote form of the enzyme but had the eukaryote form. The selective grass herbicides of the diphenoxypropionic acid type and the cyclohexanedione type, in vitro, inhibited plastidic ACCase of the eukaryote form from wheat but did not inhibit that of the prokaryote form from pea, suggesting that the origin of the tolerance of intact pea plant toward these herbicides is partly in the insensitivity of the prokaryote form of the enzyme. The origin of the susceptibility of the Gramineae plants toward these herbicides seems to lie in the presence of the herbicide-sensitive eukaryote form and the absence of the insensitive prokaryote form due to the lack of the accD gene in plastid.
乙酰辅酶A羧化酶（ACCase，EC 6.4.1.2）催化丙二酰辅酶A的合成，丙二酰辅酶A是脂肪酸合成的第一个中间产物。我们通过比较叶片和质体蛋白质提取物中两种ACCase的生物素多肽，研究了豌豆叶片中两种形式（原核生物形式和真核生物形式）的ACCase的定位。我们发现，两种形式的ACCase存在于豌豆叶片的不同细胞区室中；原核生物形式存在于质体中，真核生物形式存在于其他地方，可能在细胞质中。这一结果表明存在两个丙二酰辅酶A合成位点。禾本科植物，如水稻和小麦，其叶绿体基因组中缺乏编码原核生物形式ACCase亚基之一的accD基因，没有该酶的原核生物形式，但有真核生物形式。二苯氧基丙酸型和环己二酮型选择性禾本科除草剂在体外抑制了小麦真核生物形式的质体ACCase，但不抑制豌豆原核生物形式的ACCase，这表明完整豌豆植株对这些除草剂的耐受性部分源于该酶原核生物形式的不敏感性。禾本科植物对这些除草剂敏感的原因似乎在于存在对除草剂敏感的真核生物形式，且由于质体中缺乏accD基因而不存在不敏感的原核生物形式。
