Aldolase Does Not Show Enhanced Diffusion in Dynamic Light Scattering Experiments

Recent experimental studies have measured a 30–80% increase of the diffusion coefficient when various enzymes, including aldolase, are catalytically active. This observation has been supported by several theoretical explanations; however, other theoretical studies argue against the possibility of enhanced diffusion, and two of them ascribe the experimental observations to potential artifacts arising in fluorescence correlation spectroscopy (FCS) measurements. Here, we utilized dynamic light scattering (DLS) to measure the diffusion coefficient of aldolase in the absence and presence of its substrate. The DLS measurements have an experimental error of 3% and do not find a statistically significant change of the aldolase diffusion coefficient even at a saturating substrate concentration. This finding lends support to the contention that photophysical artifacts may have affected the FCS measurements and challenges the idea that enzymes can be self-propelled by their catalytic activity.