Kinetic enhancement of the diffusion-limited enzyme beta-galactosidase when displayed with quantum dots

Abstract

The phenomenon of enzyme catalytic enhancement when displayed on a nanoparticle surface has now become well established in the literature and has significant implications across many disciplines that rely on enzymes. It is thus essential to determine which enzymes best utilize this effect. Of particular interest is β-galactosidase, one of the best characterized enzymes which typically operates optimally at diffusion-limited rates. We couple this large tetrameric enzyme to semiconductor quantum dots (QDs) by utilizing a configuration opposite to that used previously with the QDs now displayed on the enzyme. Following physicochemical characterization of the resulting hybrid conjugates, we compared its activity to that of free enzyme. We find that, despite anticipating a seemingly hard rate ceiling, the presence of QDs around the enzyme surface results in a three-fold enhancement of catalytic rate (k_cat), suggesting a super-diffusional rate of substrate accessibility. Mechanisms that may account for these results are discussed along with potential applications for utilizing this type of enhanced catalytic configuration.