Microbial enzymatic release

Nickel removed by coprecipitation can be remobilized by microbial action under anaerobic conditions (Francis and Dodge 1990). Remobilization results Ifom enzymatic reductive dissolution of iron with subsequent release of coprecipitated metals. A lowering of pH as a result of enzymatic reactions may indirectly enhance the dissolution of nickel. Experiments using mixed precipitates with goethite... 

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) ... 

As plant tissues senesce and die, three processes may ensue almost simultaneously. First, enzymes within the dead but sterile and physically intact cells cause proteolysis and other autolytic degradations. The released amino acids, sugars, tannins, phenols, and quinones may be oxidized by chemical or enzymatic catalysis to produce humus-like pigments, or proto-humus as discussed by Stevenson in Chapter 2. This was well illustrated by Cohen (Given and Dickinson, 1975) who observed cellular material of partially polymerized eaco-anthocyanins in residues of Rhizophora mangle deposited in a mangrove swamp in Florida. The autolytic reactions may be prominent in situations where microbial decomposition is slow due to acidity, anaerobiosis, or lack of basic nutrients. 

Unstable in alkaline media. Stable in acid and neutral media. Decomposes above 150°C. Most important metabolite is CO2, formed by microbiological degradation of the phenol compounds. ty2 (river water environmental conditions) 13.5 days (pH 7.5), and (pond water 26 to 30°C) 2.3 days (pH 7.8 to 8.5), and (deionized water 27 2°C) 36 days (pH 7), and (deionized water 27 2°C) 1.2 h (pH 10). ty2 (soil) 30 to 60 days Hydrolyzed slowly in acid and alkaline media. Stable to UV light. Decomposes above 150°C. In soil, microbial degradation yields 3-chloroaniline via an enzymatic hydrolysis reaction with release of CO2. ti/2 (distilled water)... 

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