Evidence for Enzyme “Sliding” when Physisorbed on a Surface in a Multienzyme Reaction System

While the reactions of enzymes with cofactors physically or chemically attached to a surface have been demonstrated, a fundamental question that remains is how enzymes interact with the surface, specifically whether they desorb from the surface after reaction and readsorb or whether they traverse, or “slide”, across the surface. Detailed kinetic modeling of experimental results for multienzyme-coupled regeneration of the cofactor nicotinamide adenine dinucleotide (NAD⁺) tethered to the surface of silica particles (SiNPs) via a flexible tether arm shows that each enzyme performs multiple (200–400) catalytic cycles per an adsorption event on the particle surface. This suggests that the enzymes must be able to slide across the surface in a single adsorption cycle. Two coupled enzyme systems, (i) alcohol dehydrogenase (ADH) coupled with glutamate dehydrogenase (GluDH) and (ii) EcG3PD coupled with the NAD⁺ regenerating enzyme NADH oxidase from Clostridium aminovalericum, were investigated and shown to perform in a similar manner, suggesting that this is a broad phenomenon that may have implications for biochemical reactions.