The catalytic site of the pectin biosynthetic enzyme alpha-1,4-galacturonosyltransferase is located in the lumen of the Golgi.
The catalytic site of the pectin biosynthetic enzyme alpha-1,4-galacturonosyltransferase is located in the lumen of the Golgi.
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DOI：
10.1104/pp.127.1.360
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发表时间：
2001-09
期刊：
影响因子：
7.4
通讯作者：
J. Sterling;H. F. Quigley;A. Orellana;D. Mohnen
中科院分区：
文献类型：
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作者：
J. Sterling;H. F. Quigley;A. Orellana;D. Mohnen
α-1，4-半乳糖醛酸基转移酶(Galat)是植物细胞壁果胶多糖高半乳糖醛酸(HGA)生物合成所必需的一种酶。豌豆匀浆中半乳糖酶活性的研究Alaska)茎节间以线性和不连续的蔗糖梯度共同定位，具有潜在的UDPase活性，这是高尔基膜特有的酶标记。Galat活性从抗霉素A不敏感的NADH中分离出来：细胞色素c还原酶和细胞色素c氧化酶活性，分别是内质网和线粒体的酶标记。从大多数(80%)的显示质膜的标志蛋白酶K处理的高尔基体囊泡与未处理的高尔基体囊泡的Galat活性相似，而在Triton X-100存在下，用蛋白酶K处理高尔基体囊泡后，没有检测到Galat活性。这些结果表明Galat的催化中心位于高尔基体腔内。由高尔基体定位的Galat产生的产物被多聚半乳糖醛酸酶处理转化为单半乳糖醛酸和双半乳糖醛酸，从而表明Galat合成了1->；4-连接的α-D-半乳糖醛酸。我们的数据首次提供了参与HGA合成的糖基转移酶存在于高尔基体的酶证据。结合体内标记和免疫细胞化学研究的先前结果，这些结果表明果胶的生物合成发生在高尔基体中。提出了果胶多糖HGA的生物合成模型。
Alpha-1,4-galacturonosyltransferase (GalAT) is an enzyme required for the biosynthesis of the plant cell wall pectic polysaccharide homogalacturonan (HGA). GalAT activity in homogenates from pea (Pisum sativum L. var. Alaska) stem internodes co-localized in linear and discontinuous sucrose gradients with latent UDPase activity, an enzyme marker specific for Golgi membranes. GalAT activity was separated from antimycin A-insensitive NADH:cytochrome c reductase and cytochrome c oxidase activities, enzyme markers for the endoplasmic reticulum and the mitochondria, respectively. GalAT and latent UDPase activities were separated from the majority (80%) of callose synthase activity, a marker for the plasma membrane, suggesting that little or no GalAT is present in the plasma membrane. GalAT activities in proteinase K-treated and untreated Golgi vesicles were similar, whereas no GalAT activity was detected after treating Golgi vesicles with proteinase K in the presence of Triton X-100. These results demonstrate that the catalytic site of GalAT resides within the lumen of the Golgi. The products generated by Golgi-localized GalAT were converted by endopolygalacturonase treatment to mono- and di-galacturonic acid, thereby showing that GalAT synthesizes 1-->4-linked alpha-D-galacturonan. Our data provide the first enzymatic evidence that a glycosyltransferase involved in HGA synthesis is present in the Golgi apparatus. Together with prior results of in vivo labeling and immunocytochemical studies, these results show that pectin biosynthesis occurs in the Golgi. A model for the biosynthesis of the pectic polysaccharide HGA is proposed.