Microbial iron assimilation

Advantages of Enteric Bacteria for Studies of Microbial Iron Assimilation... 

In microbial iron assimilation, one mechanism for the release of iron from siderophores is the enzymatic reduction to the Fe state. Siderophore stability constants are much lower for Fe +, which has a lower charge-to-radius ratio. Moreover, ligand exchange reactions for the high-spin Fe ion are much faster than for the Fe ion. Stability constants of ferrous siderophores are experimentally difficult to obtain. Limiting pH-independent redox potentials can be utilized, however, to describe the electrochemical and chemical equilibria between fidly coordinated Fe + and Fe +-siderophore complexes and the uncomplexed Fe(H20)6 + and Fe(H20)e +, respectively, in a simple model as described in equation (5) ... 

The factors concerned with iron metabolism have been the subject of many investigations (Bothwell and Finch, 1962 Gross, 1964 Jacobs and Worwood, 1974). Aspects of the iron transporting system of mitochondria have been outlined recently (Flatmark and Romslo, 1977), while the more specialized processes involved in microbial iron assimilation have been described (Neilands, 1972,1977 Raymond, 1977). 

Roles of Iron in Microbial Physiology and Processes for Its Assimilation... 

The vertical distribution of dissolved iron in the vast majority of the ocean is similar to that of other biologically-assimilated nutrients, notably nitrate and phosphate, and characterized by the following key features (a) depletion at the surface, driven by biological uptake (b) a mid-depth maximum, correlated to the rate of export production from the photic zone and the result of microbial regeneration of exported material (c) reasonably stable, invariant concentrations at depth [71]. Iron, however, dilfers from the macronutrients in notable, sometimes surprising ways, which raise basic questions about how its nutrientlike profile is maintained (Fig. 3). 

Table 1 collects selected metric parameters and IR stretching frequencies (wno) fot a representative set of six-coordinated (6C) complexes of iron, ruthenium, and osmium, and few iron 5C-compounds. A number of Fe(III) heme proteins are involved in the regulation of the NO biosynthesis by the enzyme NO synthase, in NO transport (as vasodilator) in nitrophorins and in NO inhibition processes of cytochrome P450 and related enzymes (45). Heme enzymes are also intermediates in cyt cd nitrite reductases (NIRs), (46) and in NO reduction by a fungal cyt P450 NO reductase (47). The nonheme Fe(III) nitrile hydratase enzyme (NHase) is relevant to the microbial assimilation of organic nitriles, using... 

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