A 35 kDa monomeric purple acid phosphatase (APase) was purified from cell wall extracts of Pi starved (–Pi) Arabidopsis thaliana suspension cells and identified as AtPAP17 (At3g17790) by mass spectrometry and N-terminal microsequencing. AtPAP17 was de novo synthesized and dual-localized to the secretome and/or intracellular fraction of –Pi or salt-stressed plants, or senescing leaves. Transiently expressed AtPAP17–green fluorescent protein localized to lytic vacuoles of the Arabidopsis suspension cells. No significant biochemical or phenotypical changes associated with AtPAP17 loss of function were observed in an atpap17 mutant during Pi deprivation, leaf senescence, or salinity stress. Nevertheless, AtPAP17 is hypothesized to contribute to Pi metabolism owing to its marked up-regulation during Pi starvation and leaf senescence, broad APase substrate selectivity and pH activity profile, and rapid repression and turnover following Pi resupply to –Pi plants. While AtPAP17 also catalyzed the peroxidation of luminol, which was optimal at pH 9.2, it exhibited a low Vmax and affinity for hydrogen peroxide relative to horseradish peroxidase. These results, coupled with absence of a phenotype in the salt-stressed or –Pi atpap17 mutant, do not support proposals that the peroxidase activity of AtPAP17 contributes to the detoxification of reactive oxygen species during stresses that trigger AtPAP17 up-regulation.

中文翻译：

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拟南芥 PAP17 是一种双定位紫色酸性磷酸酶，在磷酸盐剥夺、衰老和氧化应激过程中上调

从 Pi 饥饿 (-Pi) 拟南芥悬浮细胞的细胞壁提取物中纯化 35 kDa 单体紫色酸性磷酸酶 (APase)，并通过质谱和 N 端微测序鉴定为 AtPAP17 (At3g17790)。AtPAP17 是从头合成的，并双定位于 -Pi 或盐胁迫植物或衰老叶片的分泌组和/或细胞内部分。瞬时表达的 AtPAP17-绿色荧光蛋白定位于拟南芥悬浮细胞的裂解液泡。在 Pi 剥夺、叶片衰老或盐分胁迫期间，在 atpap17 突变体中未观察到与 AtPAP17 功能丧失相关的显着生化或表型变化。然而，假设 AtPAP17 有助于 Pi 代谢，因为它在 Pi 饥饿和叶片衰老期间显着上调，广泛的 APase 底物选择性和 pH 活性曲线，以及在 Pi 重新供应给 -Pi 植物后的快速抑制和周转。虽然 AtPAP17 还催化鲁米诺的过氧化，其在 pH 9.2 时是最佳的，但相对于辣根过氧化物酶，它表现出较低的 Vmax 和对过氧化氢的亲和力。这些结果，再加上盐胁迫或-Pi atpap17 突变体中不存在表型，不支持 AtPAP17 的过氧化物酶活性有助于在触发 AtPAP17 上调的应激期间活性氧物质的解毒的提议。相对于辣根过氧化物酶，它表现出较低的 Vmax 和对过氧化氢的亲和力。这些结果，再加上盐胁迫或-Pi atpap17 突变体中不存在表型，不支持 AtPAP17 的过氧化物酶活性有助于在触发 AtPAP17 上调的应激期间活性氧物质的解毒的提议。相对于辣根过氧化物酶，它表现出较低的 Vmax 和对过氧化氢的亲和力。这些结果，再加上盐胁迫或-Pi atpap17 突变体中不存在表型，不支持 AtPAP17 的过氧化物酶活性有助于在触发 AtPAP17 上调的应激期间活性氧物质的解毒的提议。