Diffusion-limited enzyme

Enzyme rate limited by diffusion / From Wikipedia, the free encyclopedia

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A diffusion-limited enzyme catalyses a reaction so efficiently that the rate limiting step is that of substrate diffusion into the active site, or product diffusion out.[2] This is also known as kinetic perfection or catalytic perfection. Since the rate of catalysis of such enzymes is set by the diffusion-controlled reaction, it therefore represents an intrinsic, physical constraint on evolution (a maximum peak height in the fitness landscape). Diffusion limited perfect enzymes are very rare. Most enzymes catalyse their reactions to a rate that is 1,000-10,000 times slower than this limit. This is due to both the chemical limitations of difficult reactions, and the evolutionary limitations that such high reaction rates do not confer any extra fitness.[1]

Activity_distribution_graph.png
The distribution of known enzyme catalytic rates (kcat/KM). Most enzymes have a rate around 105 s−1M−1. The fastest enzymes in the dark box on the right (>108 s−1M−1) are constrained by the diffusion limit. (Data adapted from reference[1])