Interfacial enzymes

In determination of the catalytic parameters of an enzyme-catalyzed interfacial reaction, increasing amounts of substrate are added to a solution 

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Hickel, A., Radke, C.J. and Blanch, H.W. (1999) Hydroxynitrile lyase at the diisopropyl ether/water interface evidence for interfacial enzyme activity. Biotechnology and Bioengineering, 65, 425—136. 

Schmid, R.D. and Verger, R., Lipases interfacial enzymes with attractive applications. Angew. Chem. Int. Ed., 1998, 37, 1608-1633 Hasan, F., Shah, A.A. and Hameed, A., Industrial applications of microbial lipases. Enzyme. Microb. TechnoL, 2006, 39, 235-251. 

Selected entries from Methods in Enzymology [vol, page(s)] Activation of lipolytic enzymes by interfaces, 64, 341 model for lipase action on insoluble lipids, 64, 345 interfacial enzyme inactivation, 64, 347 reversibility of the adsorption step, 64, 347 monolayer substrates, 64, 349 kinetic models applicable to partly soluble amphiphilic lipids, 64, 353 surface dilution model, 64, 355 and 364 practical aspects, 64, 357. 

Lipases are triglyceride esterases, and as these substrates are insoluble in water, lipases are interfacial enzymes. Under these conditions, the hydrolytic reaction versus the synthetic reaction is favoured1. 

Schmid, R. D. Verger, R. Lipases interfacial enzymes with attractive applications. Angew. Chem. Int. Ed. 1998, 37, 1608-1633. 

In more detail, catalysis of an interfacial enzyme involves the following steps ... 

Fig. 9.3 Kinetic model illustrating the covalent inhibition of a lipolytic enzyme at a lipid/ water interface. Symbols and abbreviations are as follows A, total interfacial area (surface) V total volume (volume) E, free enzyme concentration (molecule/volume) , interfacial enzyme concentration (molecule/ surface) S, interfacial concentration of substrate (molecule/surface) I, interfacial concentration of inhibitor (molecule/surface) P, product concentration (molecule/volume) E S, interfacial enzyme-substrate complex... 

Fig. 9.16 Kinetic model illustrating the inhibition of HPL by orlistat in the aqueous phase and its reactivation at a lipid-water interface. The following symbols and abbreviations are used here E, free enzyme (molecule/volume) E, interfacial enzyme (molecule/surface) FA, fatty acid at the interface (molecule/surface) E -FA, interfacial enzyme-fatty acid complex (molecule/surface) THLc, closed reactive orlistat in the bulk (molecule/volume) THLo, open non-reactive orlistat at the interface (molecule/surface) -THLO, form 1 of cova-...

Verger, R. and de Haas, G.H. (1976) Interfacial enzyme kinetics of lipolysis. Annual Review Biophys. Bioeng. 5, 77-117... 

Schmid, A., and Dordick, J.S. (2001) Lipases interfacial enzymes with attractive applications. Nature, 409, 258-268. 

Syntheses in reverse micelles are carried out to order and orient monomers before polymerization to control further the polymer backbone, architecture, and functional properties and thereby enhance optical, mechanical, and processing properties compared with the polymers synthesized in bulk [11-16]. These membrane-templated interfacial enzyme-based polymerizations are explored to couple synthesis and processing in one step, with the formation of polymers as spheres. Experimental approaches for the enzyme-catalyzed syntheses of polymers in reverse micelles are described in the following. 

Verger, R., and G. H. de Haas. 1976. Interfacial Enzyme Kinetics of Lipolysis. Annual Review of Biophysics and Bioengineering 5 77-117. 

Figure 10.1. Binding of an interfacial enzyme to a substrate interface. Upon binding, the enzyme adopts an interfacial conformation. The kinetics of binding is described by the rate constants of binding (kon) and dissociation (koff).

The change in interfacial enzyme coverage (9) as a function of time can be expressed as... 

Normalization of the rate equation by total enzyme concentration v/ Et ) and rearrangement results in the following expression for the velocity of a reaction catalyzed by an interfacial enzyme ... 

Figure 10.3. Initial velocity vctsus intofacial area pw unit volume plot for an interfacial enzyme.

For kinetic studies of interfacial enzymes, it is necessary to determine the interfacial area of substrate present in the reaction mixture. For this purpose, light-scattering techniques are routinely used in measurement of the radius of emulsion droplets (r ). Assuming droplet sphericity, it is possible to calculate an equivalent volume from... 

Figure 10.4. Simulations of the effects of changing (a) the dissociation constant of the interfacial enzyme (Kj), (b) interfacial enzyme coverage, and (c) effective saturation surface concentration of interfacial enzyme (E ) on initial velocity versus interfacial area per unit volume patterns.

TABLE 10.1 Units for Variables Used in Analysis of the Kinetics of Interfacial Enzymes... 

Figure 10.5. Initial velocity versus total enzyme concentration plot used in determination of the effective saturation surface concentration of interfacial enzyme...

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