Kinetic Study on Enzymatic Hydrolysis of Cellulose in an Open, Inhibition-Free System.

Due to the complexity of cellulases and the requirement of enzyme adsorption on cellulose prior to reactions, it is difficult to evaluate their reaction with a general mechanistic scheme. Nevertheless, it is of great interest to come up with an approximate analytic description of a valid model for the purpose of developing an intuitive understanding of these complex enzyme systems. Herein, we used the surface plasmonic resonance method to monitor the action of a cellobiohydrolase by itself, as well as its mixture with a synergetic endoglucanase, on the surface of a regenerated model cellulose film, under continuous flow conditions. We found a phenomenological approach by taking advantage of the long steady state of cellulose hydrolysis in the open, inhibition-free system. This provided a direct and reliable way to analyze the adsorption and reaction processes with a minimum number of fitting parameters. We investigated a generalized Langmuir-Michaelis-Menten model to describe a full set of kinetic results across a range of enzyme concentrations, compositions, and temperatures. The overall form of the equations describing the pseudo-steady-state kinetics of the flow-system shares some interesting similarities with the Michaelis-Menten equation. The use of familiar Michaelis-Menten parameters in the analysis provides a unifying framework to study cellulase kinetics. The strategy may provide a shortcut for approaching a quantitative while intuitive understanding of enzymatic degradation of cellulose from top to bottom. The open system approach and the kinetic analysis should be applicable to a variety of cellulases and reaction systems to accelerate the progress in the field.

DNA-Mediated Step-Growth Polymerization of Bottlebrush Macromonomers.

Herein, we report the DNA-mediated self-assembly of bivalent bottlebrush polymers, a process akin to the step-growth polymerization of small molecule monomers. In these "condensation reactions", the polymer serves as a steric guide to limit DNA hybridization in a fixed direction, while the DNA serves as a functional group equivalent, connecting complementary brushes to form well-defined, one-dimensional nanostructures. The polymerization was studied using spectroscopy, microscopy, and scattering techniques and was modeled numerically. The model made predictions of the degree of polymerization and size distribution of the assembled products, and suggested the potential for branching at hybridization junctions, all of which were confirmed experimentally. This study serves as a theoretical basis for the polymer-assembly approach which has the potential to open up new possibilities for suprapolymers with controlled architecture, macromonomer sequence, and end-group functionalities.

Enzymatic Activities of Polycatalytic Complexes with Nonprocessive Cellulases Immobilized on the Surface of Magnetic Nanoparticles.

Polycatalytic enzyme complexes made by immobilization of industrial enzymes on polymer- or nanoparticle-based scaffolds are technologically attractive due to their recyclability and their improved substrate binding and catalytic activities. Herein, we report the synthesis of polycatalytic complexes by the immobilization of nonprocessive cellulases on the surface of colloidal polymers with a magnetic nanoparticle core and the study of their binding and catalytic activities. These polycatalytic cellulase complexes have increased binding affinity for the substrate. But due to their larger size, these complexes were unable to access to the internal surfaces of cellulose and have significantly lower binding capacity when compared to those of the corresponding free enzymes. Analysis of released soluble sugars indicated that the formation of complexes may promote the prospect of having consistent, multiple attacks on cellulose substrate. Once bound to the substrate, polycatalytic complexes tend to remain on the surface with very limited mobility due to their strong, multivalent binding to cellulose. Hence, the overall performance of polycatalytic complexes is limited by its substrate accessibility as well as mobility on the substrate surface.