Hydrolases catalytic efficiency

In summary, a broad range of large-scale applicable biocatalytic methodologies have been developed for the production of L-amino acids in technical quantities. Among these industrially feasible routes, enzymatic resolutions play an important role. In particular, L-aminoacylases, L-amidases, L-hydantoinases in combination with L-carbamoylases, and /l-lactam hydrolases are efficient and technically suitable biocatalysts. In addition, attractive manufacturing processes for L-amino acids by means of asymmetric (bio-)catalytic routes has been realized. Successful examples are reductive amination, transamination, and addition of ammonia to rx,/fun-saturated carbonyl compounds, respectively. 

My goal in this chapter is to describe the proton transfer reactions that occur during the course of hydrolase-catalyzed reactions and to provide some insight into how they contribute to the catalytic efficiency of these enzymes. Rather than pres-... 

Lipase-catalysed interesterification has found many applications in production of edible and specialty lipids due to mild reaction conditions, high catalytic efficiency, the inherent selectivity of natural catalysts and production of much purer products as compared to chemical methods (Sonnet, 1988). Lipases (hydrolases) are used for hydrolysis and ester synthesis. They are classified as non-specific or random, positional specific or 1,3-specific and acyl group- or structure-specific, depending on their activity towards fatty acids... 

Values are expressed as catalytic efficiencies V IKm) at pH 7.4 and 37 C nd, not determined. Lactase phlorizin hydrolase (LPH) was purified from sheep small intestine [40]. 

OPH has broad organophosphate hydrolase activity and is able to cleave various phosphorus-ester bonds (P-0, P-CN, P-F, P-S) (Schoheld and DiNovo 2010). Another very similar enzyme has been identified in the soil bacterium. Agrobacterium radiobacter (OpdA). Like the OPH, OpdA displays extraordinary catalytic efficiency for OPs for instance, the kcaJK of OpdA for the pesticide methyl paralhion is in the order of 3 x 10 s M (Scott et al. 2008 Bigley and Ranshel 2013). 

SxxK (3-lactamases are uncoupled SxxK acyl transferases that work as (3-lactam antibiotic hydrolases. They represent a mechanism of defence of great efficiency. On good (3-lactam substrates, their catalytic centres can turn over 1000 times per second. 

Larsson, R. Ramstrom, O. Dynamic combinatorial thiolester libraries for efficient catalytic self-screening of hydrolase substrates. Ear. J. Org. Chem. 

The atom efficiency of a kinetic resolution is increased if the starting material is not an ester but a lactone. Indeed, kinetic resolutions of lactones are used on an industrial scale. Fuji/Daiichi Chemicals produces D-pantothenic acid on a multi-ton scale based on such a resolution. D-Pantolactone is hydrolysed at pH 7 by a hydrolase from Fusarium oxysporum yielding D-pantoic acid with an ee of 96% while L-pantoic acid was barely detectable. The immobilized Fusarium oxysporum cells were recycled 180 times and retained 60% of their activity, demonstrating the great stability of this catalytic system [47-50]. 

These enzymes are promising for destruction of chemical weapons stockpiles, soil remediation, decontamination of materials, protective equipment, and water polluted by pesticides and nerve agents (Russel et al, 2003). In particular, phosphorothiolates such as VX are relatively resistant to PTE. Thus, oxidative cleavage of the P-S bond could be achieved by oxidases like laccases. These enzymes could be used in association with other OP-degrading enzymes for skin decontamination or in topical skin protection formulations. Though no work has been performed on combined action of oxidases and hydrolases, oxidation of P-bonded alkyl/aryl chains by oxidases is expected to alter enantio-selectivity of PTE for parent OPs, and therefore to improve the efficiency of catalytic bioscavengers. 

Fundamental studies of the molecular basis of cellulolytic enzymes show surface interactions are a key determinant of enzyme efficiency. Retaining and inverting mechanisms have recently been shown to have similar operations in cellulose hydrolysis as in the general-acid catalytic mechanisms of other glycolsyl hydrolases. Specific physical and chemical characteristics of the solid substrate have also been shown to influence greatly the hydrolysis rate of cellulolytic enzymes. 

Hydrolases. Hydrolytic mechanisms are also important in insecticide resistance, despite the apparent low activities in resistant insects when compared to mammalian enzymes (Table III). Some strains of resistant mosquitoes (22), Tribolium beetles (24), and Indianmeal moth (22) have specific resistance for malathion and similar carboxylester insecticides. This is due to increased catalytic hydrolysis, possibly through production of a more efficient enzyme (25.26). Californian tobacco budworms with low level permethrin resistance exhibited twice the normal activity of trans-permethrin carboxylester hydrolase (27). 

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