Institute for Multidisciplinary Research, Belgrade, Serbia.
Plant Biol (Stuttg). 2010 May 1;12(3):406-13. doi: 10.1111/j.1438-8677.2009.00237.x.
Silk of some maize genotypes contains a high level of phenolics that undergo enzymatic oxidation to form quinones, which condense among themselves or with proteins to form brown pigments. Two phenolic oxidizing enzymes, peroxidase (POD; EC 1.11.1.7) and polyphenol oxidase (PPO; EC 1.10.3.1), from maize (Zea mays L.) silk were characterised with respect to their preferred substrate, different isoforms and specific effectors. One browning silk sample with high, and two non-browning samples with low phenolic content were investigated. Although POD oxidizes a wide range of phenolic substrates in vitro, its activity rate was independent of silk phenolic content. PPO activity, detected with o-diphenolic substrates, was abundant only in browning silk, and low or absent in non-browning silk. Pollination increased POD but not PPO activity. Isoelectric-focusing (IEF) and specific staining for POD and PPO showed a high degree of polymorphism that varied with silk origin. The IEF pattern of POD revealed a number of anionic and several cationic isoenzymes, with the most pronounced having neutral pI 7 and a basic isoform with pI 10. Detected isoforms of PPO were anionic, except for one neutral form found only in browning silk, and occupied positions different from those of POD. Different inhibitory effects of NaN(3), EDTA, KCN, and L-cysteine, as well as different impacts of a variety of cations on the oxidation of chlorogenic acid, mediated by PPO or POD, were detected. The findings are discussed in terms of a possible roles of these enzymes in defence and pollination.
一些玉米基因型的丝中含有高水平的酚类物质，这些物质会发生酶促氧化形成醌，醌之间会发生缩合反应，或者与蛋白质发生缩合反应形成棕色色素。从玉米（Zea mays L.）丝中分离到两种酚氧化酶，过氧化物酶（POD；EC 1.11.1.7）和多酚氧化酶（PPO；EC 1.10.3.1），研究了它们对首选底物、不同同工酶和特定效应物的特性。一个褐变丝样品具有高酚含量，两个非褐变样品具有低酚含量。尽管 POD 在体外氧化广泛的酚类底物，但它的活性速率与丝中酚类含量无关。仅在褐变丝中检测到用邻二酚基底物检测到的 PPO 活性丰富，而在非褐变丝中则低或不存在。授粉增加了 POD 但没有增加 PPO 活性。等电聚焦（IEF）和 POD 和 PPO 的特异性染色显示出高度的多态性，其随丝的来源而变化。POD 的 IEF 模式显示了许多阴离子和几种阳离子同工酶，其中最明显的具有中性 pI 7 和碱性同工酶 pI 10。检测到的 PPO 同工酶是阴离子的，除了在褐变丝中发现的一种中性形式外，它们的位置与 POD 不同。还检测到了 NaN(3)、EDTA、KCN 和 L-半胱氨酸的不同抑制作用，以及各种阳离子对 PPO 或 POD 介导的绿原酸氧化的不同影响。这些发现是根据这些酶在防御和授粉中的可能作用进行讨论的。
