PubMed · 7724676
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F Van Breusegem, R Villarroel, M Van Montagu, D Inzé. 1995. Ascorbate peroxidase cDNA from maize.. https://doi.org/10.1104/pp.107.2.649
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Recombinant pea cytosolic ascorbate peroxidase (APX) has been characterized by resonance Raman (RR) and electronic absorption spectroscopies. The ferric and ferrous forms together with the complexes with fluoride and imidazole have been studied and compared with the corresponding spectra of cytochrome c peroxidase (CCP). Ferric APX at neutral pH is a mixture of 6- and 5-coordinate high-spin and 6-c low-spin hemes, the latter two species being dominant. The results suggest that the low-spin form derives from a water/hydroxo ligand bound to the heme iron and not from a strong internal ligand as observed in CCP at alkaline pH. Two Fe-Im stretching modes are identified, as in CCP, but the RR frequencies confirm a weaker His163-Asp208 hydrogen bond than in CCP, as suggested on the basis of the X-ray structure [Patterson, W. R., and Poulos, T. L. (1995) Biochemistry 34, 4331-4341]. The data show that CCP and APX have markedly different orientations of the vinyl substituents on the heme chromophore resulting from different steric constraints exerted by the protein matrix.
To analyze the potential of the active oxygen-scavenging system of chloroplasts, we introduced Escherichia coli catalase into tobacco chloroplasts. Photosynthesis of transgenic plants was tolerant to high irradiance under drought conditions, while the wild plants suffered severe damage in photosynthesis under the same conditions. Irrespective of responses to the stress, ascorbate peroxidase was completely inactivated both in the transgenic and wild-type plants. These findings are contrary to the established idea that the ascorbate peroxidase-mediated antioxidative system protects chloroplasts from oxidative stress.
We investigated the behavior of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APx), in potato tubers during storage at low temperature. SOD activity increased temporarily within 3 weeks and was higher at 1 degree C than at 20 degrees C. APx activity also increased more at low (1 degree C) than at higher temperatures (5 and 20 degrees C). The contents of ascorbic acid (AsA), which is the substrate of APx, decreased immediately within 3 weeks and then gradually decreased until 15 weeks. The activity of CAT, the other enzyme which can scavenge hydrogen peroxide, decreased once in the first six weeks and thereafter increased to 15 weeks. Thus, the enhancement of the active oxygen-scavenging system that was induced by low temperature in potato tubers could result not only in a decrease of AsA but also in combined increases in APx and CAT activity whose manners were different.