Isozymes of Ipomoea batatas catechol oxidase differ in catalase-like activity

Gerdemann, Carsten; Eicken, Christoph; Magrini, Annette; Meyer, Helmut E.; Rompel, Annette; Spener, Friedrich; Krebs, Bernt

doi:10.1016/s0167-4838(01)00219-9

Cited by 26 publications

(22 citation statements)

References 45 publications

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“…Two lines of evidence suggest that the predicted cleavage is accurate. First, the predicted cleavage corresponds well to the experimentally determined amino termini of multiple PPO proteins purified from other plant species (Newman et al, 1993a;Gerdemann et al, 2001;Cho et al, 2003). Second, expression of the SignalP-predicted mature, thylakoid lumen-targeted form of PPO1 in E. coli produces a protein that comigrates on SDS-PAGE with PPO protein present in the leaves of red clover.…”

Section: Discussionsupporting

confidence: 63%

Cloning and Characterization of Red Clover Polyphenol Oxidase cDNAs and Expression of Active Protein in Escherichia coli and Transgenic Alfalfa

et al. 2004

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Red clover (Trifolium pratense) leaves contain high levels of polyphenol oxidase (PPO) activity and o-diphenol substrates. Wounding of leaves during harvest and ensiling results in browning of leaf tissues from activity of PPO on the o-diphenols. In association with browning, leaf proteins remain undegraded during ensiling, presumably due to PPO-generated o-quinone inhibition of leaf proteases. We cloned three red clover PPO cDNAs, PPO1, PPO2, and PPO3, from a leaf cDNA library. Sequence comparisons among the three red clover PPO clones indicated they are 87% to 90% identical at the nucleotide level (80%-83% amino acid identity). All three encode proteins predicted to localize to the chloroplast thylakoid lumen. RNAblotting and immunoblotting experiments indicated PPO1 is expressed primarily in young leaves, PPO2 in flowers and petioles, and PPO3 in leaves and possibly flowers. We expressed mature PPO1 in Escherichia coli. A portion of the expressed protein was soluble and functional in an assay for PPO activity. We also expressed the red clover PPO cDNAs under the control of a constitutive promoter in alfalfa (Medicago sativa). The expressed red clover PPO proteins were active in alfalfa extracts as evidenced by o-diphenol-dependant extract browning and quantitative assays of PPO activity. Proteolysis in leaf extracts of alfalfa expressing red clover PPO1 was dramatically reduced in the presence of an o-diphenol compared to controls. Transgenic alfalfa expressing red clover PPO should prove an excellent model system to further characterize the red clover PPO enzymes and PPO-mediated inhibition of postharvest proteolysis in forage plants.Ensiling crops is a popular method of preserving forage for animal feed, especially in the humid northern regions of the United States. During harvesting and early stages of ensiling, plant membranes are ruptured, releasing proteolytic enzymes that rapidly degrade available substrates. Once fermentation by lactobacteria has progressed sufficiently to lower silage pH to less than about 5, proteolytic activity slows significantly. The wider the window between harvest and reaching a low pH, the more extensive is the proteolytic degradation. Unfortunately, excessive proteolysis in ensiled forages results in economic losses to farmers (Rotz et al., 1993) amounting to approximately $100 million annually. This economic loss is due to purchasing additional protein to supplement diets because of poor utilization of the nonprotein nitrogen products of proteolysis (ammonia, amino acids, and small peptides) by ruminant animals. Ruminants excrete much of this nonprotein nitrogen as urea, resulting in increasing nitrogen burdens upon the environment.For some ensiled forages, such as alfalfa (Medicago sativa), proteolytic losses are especially high with degradation of 44% to 87% of the forage protein (Papadopoulos and McKersie, 1983;Muck, 1987). By contrast, red clover (Trifolium pratense), a forage with protein content similar to alfalfa, has up to 90% less proteolysis than alfalfa during ens...

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Section: Discussionsupporting

confidence: 63%

Cloning and Characterization of Red Clover Polyphenol Oxidase cDNAs and Expression of Active Protein in Escherichia coli and Transgenic Alfalfa

et al. 2004

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“…If the reduction of O 2 by TYR during melanization reactions were to occur by successive univalent steps, ROI species such as d O 2 À , H 2 O 2 , and d OH would be produced in association with reactive semiquinones and quinones. In this context, TYR has been found to exhibit both CAT activity (conversion of H 2 O 2 to 1 2 O 2 and H 2 O) and peroxygenase activity (H 2 O 2 -dependent oxygenation of substrates) (Gerdemann et al, 2001;Yamazaki and Itoh, 2003;Yamazaki et al, 2004).…”

Section: Metalloenzymes and Site-specificity Of Cytoxic Responsesmentioning

confidence: 99%

Melanogenesis and associated cytotoxic reactions: Applications to insect innate immunity

Nappi

Christensen

2005

Insect Biochemistry and Molecular Biology

547

465

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“…C-terminal processing occurs for CO from the sweet potato Ipomoea batatas as well [32]. A crystal structure has been determined for an active 39 kDa form of I. batatas CO which is missing a C-terminal fragment, apparently as a result of in vivo proteolysis [33].…”

Section: Evidence For C-terminal Proteolytic Processingmentioning

confidence: 99%

“…age site for I. batatas CO [32,40], PPOE of Lycopersicon esculentum (cherry tomato) [41], POT32 of Solanum tuberosum tubers (potato) [42], Spinacia oleracea thylakoid PPO (spinach) [43], Triticum aestivum PPO (bread wheat) [44], V. faba PPO [18,19], and V. vinifera PPO [27] (see Table 1). The transit peptide cleavage site for many other plants has been predicted based on homology.…”

Section: Evidence For N-terminal Proteolytic Processingmentioning

confidence: 99%