Functional aspects physiological substrates

By their very nature microbial oxidations require mild, usually near physiological, conditions this can be both an advantage and a disadvantage. For example, the mild conditions often enable sensitive functional groups to remain unaltered during the oxidation (e.g. 1 above), but at the same time the use of mainly aqueous conditions precludes water sensitive substrates and can limit both the concentration of substrate and complicate the recovery of products. Experimental aspects of the use of microorganisms in oxidations have been discussed previously, -and these sources of information will provide all diat is necessary to be able to carry out a laboratory microbial oxidation. 

FIGURE 3.2 Geometric aspects of enzyme function. Let us consider a condensation reaction A + B C. To proceed, the reaction requires (1) a physical contact between A and B, and (2) a well-defined orientation of both reactants (left panel). The probability that both events occur simultaneously under physiological conditions of concentration and temperature is low. The enzyme circumvents this difficulty by providing a binding site for each substrate (site a for A, site b for B), so that both A and B are concentrated on a solid phase and, most importantly, are in the correct orientation for the condensation reaction (right panel). The active site of the enzyme may also provide catalytic groups that further accelerate the reaction. 

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