Manganese biological availability

Approximately fifteen minerals are considered nutrients calcium, chromium, cohalt, copper, iron, magnesium, manganese, molybdenum, nickel, phosphorus, selenium, silicon, tin, vanadium, and zinc) of these minerals, those in italics are essential to mammalian nutrition. Minerals, which are important for good nutrition, are supplied in an organism s diet. However, we have recently realized that the biological availability of the minerals from their food sources is also important in nutrition (J). Internal metabolism, distribution, and retention are less important factors in mineral nutrition. 

In addition to its direct inhibitory effects on production, UV may also be involved in indirect effects on oceanic new production by its effects on the biological availability and chemical reactivity of micronutrients, iron, manganese, and copper, in particular. UVR also strongly affects the production of ROS and such effects can be mediated through the reactions of ROS with trace metals such as copper and iron. The specific effects are discussed in more detail below. 

These redox reactions of Mn have important effects on its oxidation state, solubility and biological availability in natural waters. As noted above, Mn(iv) and Mn(iii) exist as insoluble oxides and Mn(iv) is the most thermodynamically stable form of manganese. Thus, as expected, Mn(iv) is the major form of Mn at great depths in the sea. In surface layers of the sea, however, almost all of the Mn exists as Mn(ii). 

Sulfur cycling is affected in a variety of ways, including UV photoinhibition of organisms such as bacterioplankton and zooplankton that affect sources and sinks of DMS and UV-initiated CDOM-sensitized photoreactions that oxidize DMS and produce carbonyl sulfide. Metal cycling also interacts in many ways with UVR via direct photoreactions of dissolved complexes and of metal oxides and indirect reactions that are mediated by photochemically-produced ROS. Photoreactions can affect the biological availability of essential trace nutrients such as iron and manganese, transforming the metals from complexes that are not readily assimilated into free metal ions or metal hydroxides that are available. Such photoreactions can enhance the toxicity of metals such as copper and can initiate metal redox reactions that transform non-reactive ROS such as superoxide into potent oxidants such as hydroxyl radicals. 

Catalysis works by making a different pathway available between the reactants and the products. This new pathway has a different mechanism and a different rate law from that of the uncatalyzed reaction. The catalyzed pathway may involve a surface reaction, as in the decomposition of hydrogen peroxide catalyzed by manganese dioxide, and in biological reactions catalyzed by enzymes. Or, the catalytic mechanism may take place in the same phase as the uncatalyzed reaction. 

Bromfield, S.M., 1958. The properties of a biologically formed manganese oxide, its availability to oats and its solution by root washings. Plant Soil, 9 325—337. 

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