Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Public Health Agency of Canada, 130 Colonnade Rd, A.L. 6501H, Ottawa, Ontario K1A 0K9, Canada.
J Exp Bot. 2022 Jan 5;73(1):382-399. doi: 10.1093/jxb/erab409.
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.
从缺磷（-Pi）拟南芥悬浮细胞细胞壁提取物中纯化出一种 35 kDa 的单体紫色酸性磷酸酶（APase），并通过质谱和 N 端微测序将其鉴定为 AtPAP17（At3g17790）。AtPAP17 是从头合成的，并且在缺磷或盐胁迫植物或衰老叶片中双重定位于分泌组和/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溶酶体中。在缺磷、叶片衰老或盐胁迫期间，atpap17 突变体中没有观察到与 AtPAP17 功能丧失相关的显著生化或表型变化。然而，由于 AtPAP17 在缺磷和叶片衰老期间显著上调，具有广泛的 APase 底物选择性和 pH 活性谱，以及在向 -Pi 植物补充 Pi 后迅速受到抑制和周转，因此假设它有助于 Pi 代谢。虽然 AtPAP17 还催化了鲁米诺的过氧化反应，其最适 pH 为 9.2，但与辣根过氧化物酶相比，它的 Vmax 和对过氧化氢的亲和力较低。这些结果，加上在盐胁迫或 -Pi atpap17 突变体中缺乏表型，不支持 AtPAP17 的过氧化物酶活性有助于在触发 AtPAP17 上调的应激中解毒活性氧的观点。
