Frenkel C, Peters J S, Tieman D M, Tiznado M E, Handa A K
Department of Plant Science, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA.
J Biol Chem. 1998 Feb 20;273(8):4293-5. doi: 10.1074/jbc.273.8.4293.
We provide genetic evidence that the production of methanol in tomato fruit is regulated by pectin methylesterase (PME, EC 3.1.1.11), an enzyme that catalyzes demethoxylation of pectins. The role of PME in methanol production in tomato fruit was examined by relating the tissue methanol content to the PME enzymatic activity in wild-type Rutgers and isogenic PME antisense fruits with lowered PME activity. In the wild-type, fruit development and ripening were accompanied by an increase in the abundance of PME protein and activity and a corresponding ripening-related increase in methanol content. In the PME antisense pericarp, the level of methanol was greatly reduced in unripe fruit, and diminished methanol content persisted throughout the ripening process. The close correlation between PME activity and levels of methanol in fruit tissues from wild-type and a PME antisense mutant indicates that PME is the primary biosynthetic pathway for methanol production in tomato fruit. Interestingly, ethanol levels that were low and unchanged during ripening of wild-type tomatoes increased progressively with the ripening of PME antisense fruit. In vitro studies indicate that methanol is a competitive inhibitor of the tomato alcohol dehydrogenase (ADH, EC 1.1.1.1) activity suggesting that ADH-catalyzed production of ethanol may be arrested by methanol accumulation in the wild-type but not in the PME mutant where methanol levels remain low.
我们提供了遗传学证据，表明番茄果实中甲醇的产生受果胶甲酯酶（PME，EC 3.1.1.11）调控，该酶催化果胶的脱甲氧基化反应。通过将野生型罗格斯番茄和PME活性降低的同基因PME反义果实中的组织甲醇含量与PME酶活性相关联，研究了PME在番茄果实甲醇产生中的作用。在野生型中，果实发育和成熟伴随着PME蛋白丰度和活性的增加，以及甲醇含量相应的与成熟相关的增加。在PME反义果皮中，未成熟果实中的甲醇水平大幅降低，且在整个成熟过程中甲醇含量持续减少。野生型和PME反义突变体果实组织中PME活性与甲醇水平之间的密切相关性表明，PME是番茄果实中甲醇产生的主要生物合成途径。有趣的是，野生型番茄成熟过程中较低且不变的乙醇水平随着PME反义果实的成熟而逐渐增加。体外研究表明，甲醇是番茄乙醇脱氢酶（ADH，EC 1.1.1.1）活性的竞争性抑制剂，这表明在野生型中，ADH催化的乙醇产生可能会因甲醇积累而受阻，但在甲醇水平保持较低的PME突变体中则不会。
