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Manganese (Mn) is an essential micronutrient with many functional roles in plant metabolism. Manganese acts as an activator and co-factor of hundreds of metalloenzymes in plants. Because of its ability to readily change oxidation state in biological systems, Mn plays and important role in a broad range of enzyme-catalyzed reactions, including redox reactions, phosphorylation, decarboxylation, and hydrolysis. Manganese(II) is the prevalent oxidation state of Mn in plants and exhibits fast ligand exchange kinetics, which means that Mn can often be substituted by other metal ions, such as Mg(II), which has similar ion characteristics and requirements to the ligand environment of the metal binding sites. Knowledge of the molecular mechanisms catalyzed by Mn and regulation of Mn insertion into the active site of Mn-dependent enzymes, in the presence of other metals, is gradually evolving. This review presents an overview of the chemistry and biochemistry of Mn in plants, including an updated list of known Mn-dependent enzymes, together with enzymes where Mn has been shown to exchange with other metal ions. Furthermore, the current knowledge of the structure and functional role of the three most well characterized Mncontaining metalloenzymes in plants; the oxygen evolving complex of photosystem II, Mn superoxide dismutase, and oxalate oxidase is summarized.

Oxalate oxidase has potential to act as an oxygen scavenger in active packaging to increase the shelf-life of food and beverages, while simultaneously producing the protective packaging gas carbon dioxide. This study shows that oxalate oxidase from barley can be immobilized with retained catalytic activity through entrapment in a latex polymer matrix. Conditions for formation of film containing oxalate oxidase have been evaluated as well as effects of storage and latex on enzyme activity, migration of enzyme in films, and the ability of the latex films to resist higher temperatures. Drying of enzyme-containing latex films at 75 °C prior to conditioning at 30 °C resulted in higher activity than drying solely at 30 °C, or drying at 95 °C or 105 °C followed by conditioning at 30 °C. Storage of films in air at 4 °C for 14 days did not negatively affect the enzymatic activity. Inclusion of catalase in films with oxalate oxidase effectively prevented release of hydrogen peroxide. The results suggest that the immobilized enzyme can successfully be used both as an oxygen scavenger and as an oxalic-acid scavenger.

The effects of ionic substances in seven industrial filtrates from kraft pulping, mechanical pulping, and sulfite pulping on the activity of oxalate oxidase from barley were investigated by pre-treatment of the filtrates with ion-exchange resins prior to enzymatic degradation of the oxalic acid in the filtrates. The pre-treatment resulted in increased oxalic acid degradation rates in all filtrates, except for one that was obtained from sulfite pulping. The possibility that lignosulfonates, which were present in the filtrate from sulfite pulping, could affect oxalate oxidase was investigated in a separate set of experiments involving four different preparations of lignosulfonates. At a lignosulfonate concentration of 50 mg/mL and a pH of 3.8, only 2–16% of the activity of oxalate oxidase remained. The results show the effects of anionic and cationic substances in bleaching filtrates on oxalate oxidase and indicate that there is an interaction between the enzyme, which has a positive net charge at pH 3.8, and the polymeric anionic lignosulfonates.

Increased recirculation of process water has given rise to problems with formation of calcium oxalate incrusts (scaling) in the pulp and paper industry and in forest biorefineries. The potential in using oxalate decarboxylase from Aspergillus niger for oxalic acid removal in industrial bleaching plant filtrates containing oxalic acid was examined and compared with barley oxalate oxidase. Ten different filtrates from chemical pulping were selected for the evaluation. Oxalate decarboxylase degraded oxalic acid faster than oxalate oxidase in eight of the filtrates, while oxalate oxidase performed better in one filtrate. One of the filtrates inhibited both enzymes. The potential inhibitory effect of selected compounds on the enzymatic activity was tested. Oxalate decarboxylase was more sensitive than oxalate oxidase to hydrogen peroxide. Oxalate decarboxylase was not as sensitive to chlorate and chlorite as oxalate oxidase. Up to 4 mM chlorate ions, the highest concentration tested, had no inhibitory effect on oxalate decarboxylase. Analysis of the filtrates suggests that high concentrations of chlorate present in some of the filtrates were responsible for the higher sensitivity of oxalate oxidase in these filtrates. Oxalate decarboxylase was thus a better choice than oxalate oxidase for treatment of filtrates from chlorine dioxide bleaching.

Oxalate-degrading enzymes were investigated with focus on potential applications in the pulp and paper industry and in active packaging. Changes introduced to make the pulp and paper industry more environmentally friendly, such as recirculation of process-water streams and elementary chlorine free bleaching of pulp, have led to increasing problems with precipitation of calcium oxalate. The potential of using enzymes for degradation of oxalic acid in industrial bleaching filtrates was explored to find a way to decrease the problem. The studies included chemical characterization and enzymatic treatments of 34 filtrates from kraft, mechanical, and sulfite pulping. Eight oxalate-degrading enzymes were included in the experiments. The treatments of the filtrates were affected by substances that inhibit oxalate-degrading enzymes. Multivariate data analysis, analytical treatment of filtrates with ion-exchange resins, and analysis of the effects of separate compounds on the enzyme activity were employed as tools to investigate inhibiting substances and groups of inhibitors. The experiments with ion-exchangers indicated that the inhibitors included anions, cations, as well as uncharged substances. Sulfite (≥1 mM) caused complete or almost complete inhibition of all oxalate-degrading enzymes so far examined, while the effects of chlorine oxyanions differed for the various enzymes investigated. A newly discovered oxalate decarboxylase was chosen for experiments performed directly in a mill producing mechanical pulp. The new enzyme degraded 70% of the oxalic acid in one hour, while the well-characterized oxalate decarboxylase from Aspergillus niger degraded <5% of the oxalic acid during the same period of time. Oxalate decarboxylase from the white-rot basidiomycete fungus Trametes versicolor was purified by using chromatographic methods and characterized with gel electrophoresis and tandem mass spectrometry. Results indicate that it is a 69-kDa heavily glycosylated enzyme wi

Oxalate oxidase catalyzes the conversion of oxalic acid and molecular oxygen to carbon dioxide and hydrogen peroxide. Oxalate-degrading enzymes are of interest for various applications including clinical analysis of the levels of oxalic acid in blood and urine and control of oxalic acid in industrial processes, such as pulp and paper manufacture. In these applications, the presence of oxyanions other than oxalate may affect the enzyme activity. The inhibitory effect of selected oxyanions on oxalate oxidase from barley was investigated. Seven out of fourteen of the compounds studied inhibited oxalate oxidase at a concentration of 1 mM. Perchlorate, chlorate and chlorite were selected for more detailed studies. The results indicate that perchlorate, chlorate and chlorite cause mixed inhibition of oxalate oxidase and that the severity of the inhibition within the series increases with the oxidation state. The apparent KM of the enzyme was 0.28 ± 0.05 mM.

Sclerotinia minor Jagger is a fungal pathogen of cultivated peanut (Arachis hypogaea L.) that can cause crop losses in excess of 50%. Fungicides are not completely effective at controlling the disease and can cost up to $311 per hectare for three applications. The ability to produce oxalic acid is necessary for the pathogenicity of some Sclerotinia spp. With little to no naturally occurring resistance to Sclerotinia blight in Arachis spp., a biotechnological approach was used to confer resistance to the disease. Peanut plants were transformed with a gene from barley encoding oxalate oxidase, an enzyme that degrades oxalic acid. Transformed peanuts showed resistance to S. minor and increased yields under disease pressure compared to the parental lines. Before the resistant varieties can be marketed, they must be reviewed and approved by the governmental regulatory system. Responsibility for regulation of transgenic plants in the U.S. is shared among the U.S. Department of Agriculture (USDA) through the Animal and Plant Health Inspection Service (APHIS), the Food and Drug Administration (FDA), and the Environmental Protection Agency (EPA). These agencies require several different data sets including molecular characterization and field studies before each transformation event can be commercialized. This project was designed to characterize three different transformation events, N70, P39 and W171. Molecular characterization included determination of insertion number, copy number, intactness of the expression cassette and stable inheritance of the transgene. N70 was found to have two insertions and two copies while W171 had one insertion with one copy. The P39 event has two insertions and two or more copies. Each of the three events was stable over multiple generations. Phenotypic comparisons of each transgenic line to the parent cultivar were carried out in field studies. Characteristics such as oxalate oxidase expression, yield and quality

We studied changes in the concentrations of ascorbate and glutathione, composition of soluble phenolics, and activity of oxalate oxidase in 75-day-old Serbian spruce plants after exposure to 5 mu M and 50 mu M cadmium for 6-48 h. The presence of OxOx activity in a conifer species is here demonstrated for the first time. Both Cd concentrations induced a decrease of OxOx activity in treated plants in comparison with the control at all sampling dates. The concentrations of reduced glutathione, its oxidized form, and reduced ascorbate in the plants decreased during 48-h treatment with cadmium. Among simple phenolics, only catechin increased significantly during Cd treatment.