Catalytic behaviors of enzymes attached to nanoparticles: the effect of particle mobility

Abstract

Nanoparticles provide an ideal remedy to the usually contradictory issues encountered in the optimization of immobilized enzymes: minimum diffusional limitation, maximum surface area per unit mass, and high effective enzyme loading. In addition to the promising performance features, the unique solution behaviors of the nanoparticles also point to a transitional region between the heterogeneous (with immobilized enzymes) and homogeneous (with soluble free enzymes) catalysis. The particle mobility, which is related to particle size and solution viscosity through Stokes-Einstein equation, may impact the reaction kinetics according to the collision theory. The mobility-activity relationship was examined through experimental studies and theoretical modeling in the present work. Polystyrene particles with diameters ranging from 110-1000 nm were prepared. A model enzyme, alpha-chymotrypsin, was covalently attached to the nanoparticles up to 6.6 wt%. The collision theory model was found feasible in correlating the catalytic activities of particles to particle size and solution viscosity. Changes in the size of particles and the viscosity of reaction media, which all affect the mobility of the enzyme catalyst, evidently altered the intrinsic activity of the particle-attached enzyme. Compared to K(M), k(cat) appeared to be less sensitive to particle size and viscosity.

Increasing the activity of immobilized enzymes with nanoparticle conjugation

“…This proves that lipase had a higher affinity or selectivity, represented by a smaller K M value, toward the substrate in the enzyme-AuNP complex, as the addition of NPs is an efficacious means of tuning the lipase-substrate association [49]. Furthermore, based on a diffusion-collision theory and Stokes-Einstein equation, the enzymatic activity of lipase-AuNPs conjugates is size dependent: smaller particle size resulted in a higher catalytic efficiency of lipase by increasing its kinetic affinity toward the substrate [30,50 ].…”

“…Additionally, the mobility of the NPs themselves enhances substrate-to-enzyme interactions via Brownian motion [30] while secondary interactions at the NP-enzyme interface, due in part to substrate-NP attraction through forces such as electrostatic attraction, can also increase the activity of NP immobilized enzymes [31]. In other words, enhanced activity can be attributed to the fact that with each collision between NP-immobilized enzymes and free-floating substrate, the weak association between the substrate and the NP interface results in multiple binding occurrences on one NP before the substrate moves elsewhere [31].…”

Inorganic nanomaterial-based biocatalysts

“…It also can serve as supporting materials for enzyme immobilization because carbon nanotubes can be broadly functionalized and have good dispersion in solution compared to other nanomaterials (19,20). Highly efficient enzyme loading was reported by using single-wall carbon nanotubes without requiring enzyme purification for immobilization (21).…”

Fabrication and Characterization of Core-Shell Magnetic Chitosan Nanoparticles as a Novel carrier for Immobilization of <i>Burkholderia cepacia</i> Lipase

“…Various micro/nano carriers, particularly nanoparticles and nanofibers, have become available for enzyme immobilization 4,5 . Typically, smaller particles provide a larger surface area for the attachment of enzymes 6 and a shorter diffusional path for the substrates. Thus, nanostructured carriers have been utilized as carriers for enzyme immobilization 7 .…”