Organic solution enzyme interactions

Organic solvents can interact with enzymes in several ways. There can be specific interactions between isolated solvent molecules and enzyme molecules. This kind of interaction also occurs in water containing dissolved solvent molecules. When a separate organic solvent phase is present, interfacial inactivation can also occur. This is sometimes called phase toxicity [55] to distinguish it from the molecular toxicity of isolated solvent molecules. Interfacial inactivation can be studied in detail by bubbling solvent through an aqueous enzyme solution under controlled conditions [56]. 

There is another type of enzyme mimics that provide a substrate-binding site as a result of self-aggregation of functional elements through noncovalent intermolecular interactions in solution reversed micelles in organic solutions, and micelles and lipid bilayer membranes in aqueous media. 

The simplest way to prepare a biocatalyst for use in organic solvents and, at the same time, to adjust key parameters, such as pH, is its lyophilization or precipitation from aqueous solutions. These preparations, however, can undergo substrate diffusion limitations or prevent enzyme-substrate interaction because of protein-protein stacking. Enzyme lyophilization in the presence of lyoprotectants (polyethylene glycol, various sugars), ligands, and salts have often yielded preparations that are markedly more active than those obtained in the absence of additives [19]. Besides that, the addition of these ligands can also affect enzyme selectivity as follows. 

Another consequence of application of organic solvents as a reaction medium is associated with the mechanism of enzyme-catalyzed transformations. According to the commonly accepted mechanism, the first product of the interaction of a hydrolytic (serine) enzyme with an ester is an O-acylenzyme (Scheme 5.4). When the reaction is performed in an aqueous solution, water acts as a nucleophile in the next step, to give acid B. If more nucleophilic hydrogen peroxide is present in the reaction mixture, peroxycarboxylic acids C are formed. However, in organic solvents the O-acylenzyme also reacts readily with other nucleophiles, such as... 

All soil metabolic proce.sses are driven by enzymes. The main sources of enzymes in soil are roots, animals, and microorganisms the last are considered to be the most important (49). Once enzymes are produced and excreted from microbial cells or from root cells, they face harsh conditions most may be rapidly decomposed by organisms (50), part may be adsorbed onto soil organomineral colloids and possibly protected against microbial degradation (51), and a minor portion may stand active in soil solution (52). The fraction of extracellular enzyme activity of soil, which is not denaturated and/or inactivated through interactions with soil fabric (51), is called naturally stabilized or immobilized. Moreover, it has been hypothesized that immobilized enzymes have a peculiar behavior, for they might not require cofactors for their catalysis. 

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