Diffusion-limited enzyme

Diffusion-limited enzyme

A diffusion-limited enzyme <a href="/en/Catalysis" title="Catalysis" class="wl">catalyses</a> a reaction so efficiently that the <a href="/en/Rate_limiting_step" title="Rate limiting step" class="mw-redirect wl">rate limiting step</a> is that of <a href="/en/Enzyme_substrate" title="Enzyme substrate" class="mw-redirect wl">substrate</a> <a href="/en/Diffusion" title="Diffusion" class="wl">diffusion</a> into the <a href="/en/Active_site" title="Active site" class="wl">active site</a>, or <a href="/en/Product_(chemistry)" title="Product (chemistry)" class="wl">product</a> diffusion out.<a href="#cite_note-2" style="counter-reset: mw-Ref 2;">[2]</a> This is also known as kinetic perfection or catalytic perfection. Since the rate of catalysis of such <a href="/en/Enzymes" title="Enzymes" class="mw-redirect wl">enzymes</a> is set by the <a href="/en/Diffusion-controlled_reaction" title="Diffusion-controlled reaction" class="wl">diffusion-controlled reaction</a>, it therefore represents an intrinsic, physical constraint on evolution (a maximum peak height in the <a href="/en/Fitness_landscape" title="Fitness landscape" class="wl">fitness landscape</a>). 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 <a href="/en/Fitness_(biology)" title="Fitness (biology)" class="wl">fitness</a>.<a href="#cite_note-Bar-Even_4402–10-1" style="counter-reset: mw-Ref 1;">[1]</a>

<div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none" about="#mwt1">Enzyme rate limited by diffusion</div>
<figure class="wiki-thumb"><a href="/en/File:Activity_distribution_graph.png" class="mw-file-description image media-thumb" data-hash="File:Activity_distribution_graph.png"><img loading="lazy" src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8d/Activity_distribution_graph.png/300px-Activity_distribution_graph.png" decoding="async" data-file-width="586" data-file-height="450" data-file-type="bitmap" height="230" width="300" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8d/Activity_distribution_graph.png/450px-Activity_distribution_graph.png 1.5x, //upload.wikimedia.org/wikipedia/commons/8/8d/Activity_distribution_graph.png 2x" alt="Activity_distribution_graph.png"></a><figcaption>The distribution of known <a href="/en/Enzyme_kinetics" title="Enzyme kinetics" class="wl">enzyme catalytic rates</a> (kcat/KM). Most enzymes have a rate around 105 s−1M−1. The fastest enzymes in the dark box on the right (&gt;108 s−1M−1) are constrained by the diffusion limit. (Data adapted from reference<a href="#cite_note-Bar-Even_4402–10-1" style="counter-reset: mw-Ref 1;">[1]</a>)</figcaption></figure>

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. 