Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba, Sendai, Miyagi, 980-8577, Japan.
Amino Acids. 2012 Feb;42(2-3):867-76. doi: 10.1007/s00726-011-1002-3. Epub 2011 Jul 28.
Polyamine oxidases (PAOs) are FAD-dependent enzymes involved in polyamine (PA) catabolism. Recent studies have revealed that plant PAOs are not only active in the terminal catabolism of PAs as demonstrated for maize apoplastic PAO but also in a polyamine back-conversion pathway as shown for most Arabidopsis PAOs. We have characterized Oryza sativa PAOs at molecular and biochemical levels. The rice genome contains 7 PAO isoforms that are termed OsPAO1 to OsPAO7. Of the seven PAOs, OsPAO3, OsPAO4, and OsPAO5 transcripts were most abundant in 2-week-old seedlings and mature plants, while OsPAO1, OsPAO2, OsPAO6, and OsPAO7 were expressed at very low levels with different tissue specificities. The more abundantly expressed PAOs--OsPAO3, OsPAO4, and OsPAO5--were cloned, and their gene products were produced in Escherichia coli. The enzymatic activities of the purified OsPAO3 to OsPAO5 proteins were examined. OsPAO3 favored spermidine (Spd) as substrate followed by thermospermine (T-Spm) and spermine (Spm) and showed a full PA back-conversion activity. OsPAO4 substrate specificity was similar to that of OsPAO5 preferring Spm and T-Spm but not Spd. Those enzymes also converted Spm and T-Spm to Spd, again indicative of PA back-conversion activities. Lastly, we show that OsPAO3, OsPAO4, and OsPAO5 are localized in peroxisomes. Together, these data revealed that constitutively and highly expressed O. sativa PAOs are localized in peroxisomes and catalyze PA back-conversion processes.
多胺氧化酶（PAOs）是依赖黄素腺嘌呤二核苷酸（FAD）的酶，参与多胺（PA）的分解代谢。最近的研究表明，植物 PAOs 不仅在 PA 的末端分解代谢中具有活性，如玉米质外体 PAO 所证明的那样，而且在多胺反向转化途径中也具有活性，如大多数拟南芥 PAOs 所证明的那样。我们已经在分子和生化水平上对水稻 PAOs 进行了表征。水稻基因组包含 7 种 PAO 同工型，分别称为 OsPAO1 到 OsPAO7。在这 7 种 PAOs 中，OsPAO3、OsPAO4 和 OsPAO5 的转录本在 2 周龄幼苗和成熟植株中最为丰富，而 OsPAO1、OsPAO2、OsPAO6 和 OsPAO7 的表达水平非常低，具有不同的组织特异性。表达更为丰富的 PAOs--OsPAO3、OsPAO4 和 OsPAO5--被克隆，并在大肠杆菌中表达其基因产物。纯化的 OsPAO3 至 OsPAO5 蛋白的酶活性进行了检测。OsPAO3 优先以亚精胺（Spd）为底物，其次是热精胺（T-Spm）和精胺（Spm），并具有完整的 PA 反向转化活性。OsPAO4 的底物特异性与 OsPAO5 相似，优先选择 Spm 和 T-Spm，但不选择 Spd。这些酶也将 Spm 和 T-Spm 转化为 Spd，再次表明具有 PA 反向转化活性。最后，我们表明 OsPAO3、OsPAO4 和 OsPAO5 定位于过氧化物酶体中。总之，这些数据表明，水稻中组成型和高表达的 PAO 定位于过氧化物酶体中，并催化 PA 反向转化过程。
