Photosynthesis, superoxide dismutases

Copper is one of the twenty-seven elements known to be essential to humans (69—72) (see Mineral nutrients). The daily recommended requirement for humans is 2.5—5.0 mg (73). Copper is probably second only to iron as an oxidation catalyst and oxygen carrier in humans (74). It is present in many proteins, such as hemocyanin [9013-32-3] galactose oxidase [9028-79-9] ceruloplasmin [9031 -37-2] dopamine -hydroxylase, monoamine oxidase [9001-66-5] superoxide dismutase [9054-89-17, and phenolase (75,76). Copper aids in photosynthesis and other oxidative processes in plants. 

Many metabolic processes such as glycolysis, Krebs cycle reactions, photosynthesis, protein synthesis, and lipid metabolism are affected by exposure to F. Much of the action of F on these processes can be attributed to F-dependent inhibition of enzymes. Examples of enzymes shown to be inhibited by F include enolase, phosphoglucomutase, phosphatase, hexokinase, PEP carboxylase, pyruvate kinase, succinic dehydrogenase, malic dehydrogenase, pyrophosphatase, phytase, nitrate reductase, mitochondrial ATPase, urease (Miller et al. 1983), lipase (Yu et al. 1987), amylase (Yu et al. 1988), invertase (Yu 1996 Ouchi et al. 1999), and superoxide dismutase (SOD) (Wilde and Yu 1998). 

Because of the large gradients in trace metal concentrations between the open ocean and coastal waters, oceanic phytoplankton species have evolved the ability to grow at much lower available concentrations of iron, zinc, and manganese. In doing so they have been forced to rearrange their metabolic architecture (e.g., in the case of iron-rich protein complexes involved in photosynthesis) or to switch from scarce elements to more abundant ones in some critical metalloenzymes (e.g., Ni and Mn replacement of Fe in the antioxidant enzyme superoxide dismutase). 

Superoxide dismutase, SOD (54), contains copper and zinc in one subunit. The superoxide anion, 02 , is produced by the reduction of oxygen during respiration in all living species and photosynthesis reactions in plants. This radical anion is toxic probably via the formation of peroxonitrite (54) and hydrogen peroxide (54). Superoxide dismutase functions as an antioxidant via a catalytic reaction (reaction (38)) ... 

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