Proton Transport as a Missing Design Variable in Immobilized Enzyme Catalysis.

Abstract

Carbonic anhydrase is among the fastest known enzymes, yet its performance after immobilization remains difficult to rationalize. Conventional immobilization design emphasizes stability, enzyme loading, and mass transfer while largely neglecting proton transport. In soluble carbonic anhydrase, proton transfer can limit catalytic turnover under defined pH and buffer conditions. We propose that immobilization may introduce an additional, condition-dependent resistance at the enzyme-support interface. Surface chemistry and wettability influence interfacial water organization, potentially altering hydrogen-bond dynamics and proton mobility. Strongly hydrophobic interfaces may disrupt hydration continuity, whereas strongly water-binding surfaces may restrict water reorientation and exchange, suggesting a system-dependent intermediate wettability window. We further introduce the concept of a surface proton antenna, in which appropriately positioned proton-relay groups could extend the enzyme's intrinsic pathway through interfacial water. This hypothesis must be distinguished from effects of enzyme orientation, conformational changes, substrate diffusion, confinement, buffer capacity, local pH, and product accumulation. Using carbonic anhydrase as a mechanistic model, this perspective reframes immobilization supports as potentially active components of proton-coupled catalytic interfaces and identifies interfacial proton transport as a testable design variable for CO2 conversion and other biocatalytic processes.