Reduced cellulose accessibility slows down enzyme-mediated hydrolysis of cellulose

Enzyme-mediated hydrolysis of cellulose always starts with an initial rapid phase, which gradually slows down, sometimes resulting in incomplete cellulose hydrolysis even after prolonged incubation. Although mechanisms such as end-product inhibition are known to play a role, the predominant mechanism appears to be reduced cellulose accessibility to the enzymes. When using Simon's stain to quantify accessibility, the accessibility of mechanically disintegrated and phosphoric acid-swollen cellulose substrates decreased as hydrolysis proceeded. In contrast, the poor initial accessibility of Avicel remained low throughout hydrolysis. However, washing the residual cellulose increased cellulose accessibility, likely due to the removal of tightly bound but non-productive enzymes which blocked access to more active enzymes in solution. Atomic force microscopy (AFM) analysis of the initial and residual cellulose collected when the hydrolysis plateaued, showed an increase in the roughness of the cellulose surface, possibly resulting in the tighter binding of less active cellulases.

Automated summary

Enzyme-mediated cellulose hydrolysis initially proceeds rapidly but gradually slows down, leading to incomplete hydrolysis even after prolonged incubation. The main mechanism for this appears to be reduced accessibility of cellulose to the enzymes. Washing residual cellulose increases accessibility by removing tightly bound non-productive enzymes, while atomic force microscopy analysis shows increased roughness of the cellulose surface during hydrolysis, potentially leading to tighter binding of less active cellulases.