Function of Boron at the interface between cell walls-cell membrane

我们已经发现，必需的植物营养元素硼（B）的工程交联果胶多糖链在鼠李糖半乳糖醛酸聚糖II（RG-II）的网站沿着链。在交联中，Ca^2+离子也参与连接链。Ca^2+被认为与聚半乳糖醛酸的羧基离子结合.多聚半乳糖醛酸通过高尔基体囊泡以甲基酯化形式分泌。在分泌后的细胞壁中，甲基部分被果胶甲基酯酶（PME）水解成游离羧基。在本研究中，我集中研究了各种植物来源的PME，PME酶都定位于培养的烟草细胞、豌豆茎和胡萝卜根的细胞壁中。它们由几种同工酶组成。在烟草细胞中，几乎所有的酶在等电点（IP）下都是碱性的，而胡萝卜中70%的酶在IP下是中性的。所有的PME酶都需要Ca^<2+>才能发挥活性，计算出Ca^<2+>的Km值为3 mM。硼不能激活该酶。烟草的一种基本同工酶正在提纯中。

We have revealed that the essential plant nutrient element boron (B) works to cross-link pectic polysaccharide chains at the rhamnogalacturonan II (RG-II) sites along the chain. In the cross-link, Ca^<2+> ions are also involved to connect the chains. Ca^<2+> are considered to bind ionically with the carboxyl groups of polygalacturonic acids. Polygalacturonic acids are secreted through Golgi vesicles as in a methyl-esterified form. In cell walls after secretion, the methyl moiety is hydrolyzed with pectin methyl esterase (PME) to prodtuce free carboxylic group. In this study, I have concentrated on the PME of various plant sources.PME enzymes are all localized in cell walls of cultured tobacco cells, pea stems and carrot roots. They are comprised of several isoenzymes. In tobacco cells, nearly all the enzymes are basic in the isoelectric point (IP), on the other hand 70% of the carrot enzymes are neutral in IP.All the PME enzymes need Ca^<2+> for their activities, and the Km values for Ca^<2+> were calculated to be 3 mM.Boron did not activate the enzyme. One of the basic isoenzymes of tobacco is now under purification.