Sano S, Ueda M, Kitajima S, Takeda T, Shigeoka S, Kurano N, Miyachi S, Miyake C, Yokota A
Research Institute of Innovative Technology for the Earth, Kizu, Kyoto, 619-0292 Japan.
Plant Cell Physiol. 2001 Apr;42(4):433-40. doi: 10.1093/pcp/pce054.
Galdieria partita, a unicellular red alga isolated from acidic hot springs and tolerant to sulfur dioxide, has at least two ascorbate peroxidase (APX) isozymes. This was the first report to demonstrate that two isozymes of APX are found in algal cells. Two isozymes were separated from each other at the hydrophobic chromatography step of purification and named APX-A and APX-B after the elution order in the chromatography. APX-B accounted for 85% of the total activity. Both isozymes were purified. APXs from Galdieria were monomers whose molecular weights were about 28,000, similar to stromal APX of higher plants. APX-A cross-reacted with monoclonal antibody raised against APX of Euglena gracilis in immunoblotting, but APX-B did not, although the antibody can recognize all other APXs tested. The amino-terminal sequences of APX-A and -B from Galdieria had some homology with each other but little homology with those from other sources. Their Km values for ascorbate and hydrogen peroxide were comparable with those of APX from higher plants. Unlike the green algal enzymes, the donor specificities of Galdieria APXs were as high as those of plant chloroplastic APX. On the contrary, these APXs reduced tertiary-butyl hydroperoxide as an electron acceptor as APXs from Euglena and freshwater Chlamydomonas do. The inhibition of APX-A and -B by cyanide and azide, and characteristics of their light absorbance spectra indicated that they were heme peroxidases.
加尔迪衣藻（Galdieria partita）是一种从酸性温泉中分离出来且耐受二氧化硫的单细胞红藻，它至少有两种抗坏血酸过氧化物酶（APX）同工酶。这是首次报道在藻类细胞中发现两种APX同工酶。在纯化的疏水色谱步骤中，两种同工酶彼此分离，并根据色谱中的洗脱顺序分别命名为APX-A和APX-B。APX-B占总活性的85%。两种同工酶均被纯化。加尔迪衣藻的APX是单体，其分子量约为28,000，与高等植物的基质APX相似。在免疫印迹中，加尔迪衣藻的APX-A与针对纤细裸藻APX产生的单克隆抗体发生交叉反应，但APX-B没有，尽管该抗体可以识别所有其他测试的APX。加尔迪衣藻APX-A和 -B的氨基末端序列彼此有一些同源性，但与其他来源的同源性很小。它们对抗坏血酸和过氧化氢的Km值与高等植物的APX相当。与绿藻酶不同，加尔迪衣藻APX的供体特异性与植物叶绿体APX一样高。相反，这些APX像来自裸藻和淡水衣藻中的APX一样，将叔丁基过氧化氢作为电子受体进行还原。APX-A和 -B受氰化物和叠氮化物的抑制，以及它们吸光光谱的特征表明它们是血红素过氧化物酶。
