Crowding–induced Uncompetitive Inhibition of Lactate Dehydrogenase: Role of Entropic Pushing.

The cell is an extremely complex environment, notably highly crowded, segmented and confining. Overall, there is overwhelming and ever-growing evidence that, to understand how biochemical reactions proceed in vivo, one cannot separate the biochemical actors from their environment. Effects such as excluded volume, obstructed diffusion, weak non-specific interactions and fluctuations all team up to steer biochemical reactions often very far from what observed in ideal conditions. In this paper we use Ficoll PM70 and PEG 6000 to build artificial crowded milieux of controlled composition and density in order to assess how such environments influence the bio-catalytic activity of lactate dehydrogenase (LDH). Our measurements show that the normalized apparent affinity and maximum velocity decrease in the same fashion, a behavior reminiscent of uncompetitive inhibition, with PEG resulting in the largest reduction. In line with previous studies on other enzymes of the same family, and in agreement with the known ...