Microbially Catalyzed Reactions

When biochemical reactions are studied with time, two situations commonly occur. One is when enzyme concentrations remain constant (the biological population 

Michaelis and Menten found that the rate of substrate disappearance with time could be expressed as 

When the substrate concentration is much smaller than Km, the denominator of Eq.3. 59 reduces to Km and the reaction rate, at constant enzyme concentration, is first order with respect to the substrate concentration [S]  

This equation describes the steep portion of the curve near the origin in Fig. 3.1 la. When [S] is much larger than Km, Eq. 3.60 reduces to 

FIGURE 3.11. Change of reaction rate (A) with a rate factor according to the Michaelis-Menten kinetics and (B) with time and population response. 

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In considering the energetics of a microbially catalyzed reaction, it is important to recall that progress of the redox reaction (e.g., Reaction 18.7) is coupled to synthesis of ATP within the cell, so the overall reaction is the redox reaction combined with ATP synthesis. The free energy liberated by the overall reaction is the energy liberated by the redox reaction, less that consumed to make ATP. The overall reaction s equilibrium point is where this difference vanishes at this point,... 

Reductive dehalogenation is a mechanism for the anaerobic biotransformation of chlorinated hydrocarbons such as hexachlorobenzene (HCB). In reductive dehalogenation, the halogenated compound serves as the electron acceptor rather than the donor that requires a separate carbon source. In a microbially catalyzed reaction, a halide ion is replaced by a hydrogen ion (Figure 13.7). The removal of halide ions results in compounds that are generally easier to degrade, and, in some instances, are completely mineralized. 

Figure 4 Microbially catalyzed reactions involved in the cleavage of carbon-phosphorus linkages. Modified and redrawn after Ref. [34].

It is the aim of this chapter to cover all of the literature from the beginning of the 1980s to the middle of 1998 related to enzyme- and microbial-catalyzed reactions that lead to steroids and their analogs. The subject is treated in a very practical way and the presentation offers abundant tables, schemes, and structures. The work covered in each section is classified by date. 

Increasingly, biochemical transformations are used to modify renewable resources into useful materials (see Microbial transformations). Fermentation (qv) to ethanol is the oldest of such conversions. Another example is the ceU-free enzyme catalyzed isomerization of glucose to fmctose for use as sweeteners (qv). The enzymatic hydrolysis of cellulose is a biochemical competitor for the acid catalyzed reaction. 

We can, therefore, reasonably expect the degradation to behave as an enzymatically catalyzed reaction in which phenol is the substrate and the microbial consortium serves as the enzyme. As discussed in Chapter 17, reaction rate in this case can be represented as,... 

In essence, an enzyme-catalyzed equivalent exists for almost every type of chemically catalyzed reaction, and thousands of these have been documented in comprehensive monographs and reviews (9-26). Many reactions have been observed in relatively specialized areas, particularly with groups of organic compounds such as the steroids, other terpenoids, antibiotics, aromatics, and alkaloids. Specific chemical reactions have been accomplished with intact and growing microbial cells, with plant and mammalian tissue preparations, and with... 

Microbial biofuel cells were the earliest biofuel cell technology to be developed, as an alternative to conventional fuel cell technology. The concept and performance of several microbial biofuel cells have been summarized in recent review chapters." The most fuel-efficient way of utilizing complex fuels, such as carbohydrates, is by using microbial biofuel cells where the oxidation process involves a cascade of enzyme-catalyzed reactions. The two classical methods of operating the microbial fuel cells are (1) utilization of the electroactive metabolite produced by the fermentation of the fuel substrate " and (2) use of redox mediators to shuttle electrons from the metabolic pathway of the microorganism to the electrodes. ... 

Once In an evaporation bed, a pesticide can adsorb to a soil colloid, undergo chemical or microbial degradation, or escape from the bed by volatilization. An evaporation bed has the potential advantage over an open pond of decreasing pesticide volatilization while allowing for Increased degradation through microbial and soil-catalyzed reactions. 

These processes are catalyzed by bacteria and probably involve both inorganic and organic iron and manganese species (22). They may also be strongly controlled by microbial competition between Fe(III) and sulfate-reducing bacteria (27). Associated with these reduction reactions is the reduction of residual sulfate (produced in the oxic zone by bacterially catalyzed reactions) similar to eq 7 (21). 

Lovley, D.R., F.H. Chapelle, and J.C. Woodward. 1994. Use of dissolved H2 concentrations to determine distribution of microbially catalyzed redox reactions in anoxic groundwater. Environ. Sci. Technol. 28, 1205-1210. 

Microbial kinetics14 26 can be separated in four distinct levels at the molecular or enzyme, the macromolecular or cell component, cellular, and population level. Because each level has its own unique characteristics, different kinetic treatments are needed. Moreover, the environment in which these reactions take place also affects the kinetics. For example, reactions at the molecular/ enzyme level involve enzyme-catalyzed reactions. When these reactions occur in solution, their kinetic behavior is similar to that of homogeneous catalyzed chemical reactions as described in Chapter 31. However, when enzymes are attached to inert solid supports or contained within a solid cell... 

Fig. 20 Microbially catalyzed redox reactions in dependence on pE/EH value (after Stumm and Morgan 1996)...

Oh M, Yamada T, Eiattori M, Goto S, Kanehisa M. Systematic analysis of enzyme-catalyzed reaction patterns and prediction of microbial biodegradation pathways. J. Chem. Inf Model 2007 47 1702-1712. 

Sulfide-mineral oxidation by microbial populations has been postulated to proceed via direct or indirect mechanisms (Tributsch and Bennett, 1981a,b Boon and Heijnen, 2001 Fowler, 2001 Sand et al., 2001 Tributsch, 2001). In the direct mechanism, it is assumed that the action taken by the attached cell or bacterium on a metal sulfide will solubilize the mineral surface through direct enzymatic oxidation reactions. The sulfur moiety on the mineral surface is oxidized to sulfate without the production of any detectable intermediates. The indirect mechanism assumes that the cell or bacteria do not act directly on the sulfide-mineral surface, but catalyze reactions proximal to the mineral surface. The products of these bacterially catalyzed reactions act on the mineral surfaces to promote oxidation of the dissolved Fe(II) and S° that are generated via chemical oxidative processes. Ferrous iron and S°, present at the mineral surface, are biologically oxidized to Fe(III) and sulfate. Physical attachment is not required for the bacterial catalysis to occur. The resulting catalysis promotes chemical oxidation of the sulfide-mineral surface, perpetuating the sulfide oxidation process (Figure 1). 

The liquid phase NMR spectra comprise the first direct spectroscopic evidence differentiating phenoloxidase- and metal-catalyzed reactions from noncatalyzed nucleophilic addition reactions of aniline with humic substances. The solid state NMR spectra provide the first direct evidence for nucleophilic addition of aniline to quinone and other carbonyl groups in the organic matter of whole soil and peat. The NMR approach has potential for further investigation of the effects of reaction conditions on the incorporation of aromatic amines into naturally occurring organic matter, and for studies on how aromatic amines covalently bound to organic matter may ultimately be re-released or remineralized, either chemically or microbially. 

Catalysis by enzymes requires an empirical interpretation of reaction rates because it is difficult to transfer generalizations derived from laboratory experiments to natural waters when the reaction rates are microbially catalyzed. At the present state of our knowledge, the most pressing problem is to determine which... 

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