Biocatalyst-substrate interaction

What, if anything, needs to be done to facilitate biocatalyst-substrate interaction ... 

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. 

The Michaelis-Menten equation (8.8) and the irreversible Uni Uni kinetic scheme (Scheme 8.1) are only really applicable to an irreversible biocatalytic process involving a single substrate interacting with a biocatalyst that comprises a single catalytic site. Hence with reference to the biocatalyst examples given in Section 8.1, Equation (8.8), the Uni Uni kinetic scheme is only really directly applicable to the steady state kinetic analysis of TIM biocatalysis (Figure 8.1, Table 8.1). Furthermore, even this statement is only valid with the proviso that all biocatalytic initial rate values are determined in the absence of product. Similarly, the Uni Uni kinetic schemes for competitive, uncompetitive and non-competitive inhibition are only really applicable directly for the steady state kinetic analysis for the inhibition of TIM (Table 8.1). Therefore, why are Equation (8.8) and the irreversible Uni Uni kinetic scheme apparently used so widely for the steady state analysis of many different biocatalytic processes A main reason for this is that Equation (8.8) is simple to use and measured k t and Km parameters can be easily interpreted. There is only a necessity to adapt catalysis conditions such that... 

Several experiments using different organic solvents in different biphasic media are necessary to find the adequate distribution of the reaction components. A series of experiments are essential for the choice of a process and for scaling-up. Experiments using Lewis cells [44] may yield useful results for understanding equilibrium, kinetics, and interactions between organic solvent-substrate and/or organic solvent-biocatalyst. A study of two-liquid phase biotransformation systems is detailed below in Sections II-IX. 

For enzyme catalysis to occur the biocatalyst must be complementary to the reaction transition state so that weak non-covalent interactions can be formed in the ES complex. These interactions maximize when the substrate reaches the transition state. The binding energy released in the interactions (Figure 3) partially compensates the energy required to reach the top of the... 

The addition of cofactors to antibodies is a sure means to confer a catalytic activity to them insofar as this cofactor is responsible for the activity. Indeed for many enzymes, the interaction with cofactors such as thiamins, flavins, pyridoxal phosphate, and ions or metal complexes is absolutely essential for the catalysis. It is thus a question there of building a new biocatalyst with two partners the cofactor responsible for the catalytic activity, and the antibody which binds not only the cofactor but also the substrate that it positions in a specific way one with respect to the other, and can possibly take part in the catalysis thanks to some of its amino acids. 

The selectivity is caused not only by the electronic properties of the substrates which are dependent on the nature of their substituents, as is the case in the chemical cross-benzoin condensation. Rather, steric demands of the aldehyde substituents and interactions of these with the active site of the biocatalyst, which (obviously) is different for each enzyme used, are also of significance. 

Biocatalyst inhibitors I are substrate-like molecules that interact with a given biocatalyst and interfere with the progress of biocatalysis. Inhibitors usually act in one of three ways, either by competitive inhibition, non-competitive inhibition or uncompetitive inhibition. The mode of inhibition is different in each case and as a result a different steady state kinetic scheme is required to account for each mode of inhibition. Consequently, each mode of inhibition is characterised by a different steady state kinetic equation that gives rise to a different graphical output of V versus [S] data, as we will show below. These substantial differences in graphical output can be used to diagnose the type of inhibition if unknown. 

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