Enhanced diffusion and oligomeric enzyme dissociation

The concept that catalytic enzymes can act as molecular machines transducing chemical activity into motion has concep-tual and experimental support, but experimental support has involved oligomeric enzymes, often studied under conditions where the substrate concentration is higher than biologically relevant and accordingly exceeds kM, the Michaelis constant. Urease, a hexamer of subunits, has been considered to be the gold standard demonstrating enhanced diffusion. Here we show that urease and certain other oligomeric enzymes dissociate above kM into their subunits that diffuse more rapidly, thus providing a simple physical mechanism that contributes to enhanced diffusion in this regime of concentrations. Mind-ful that this conclusion may be controversial, our findings are supported by four independent analytical techniques, static light scattering, dynamic light scattering (DLS), size-exclusion chromatography (SEC), and fluorescence correlation spectros-copy (FCS). Data for urease are emphasized and the ...