Do enzymes chase their prey?

Do enzymes chase their prey? At first thought, this seems ridiculous. However people have been measuring diffusion of substances in water for over a century. Even Einstein worked on it (his paper on Brownian motion). So it’s fairly easy to measure the diffusion of an enzyme in water. Several enzymes (catalase — one of the most efficient enzymes known, and urease) diffuse faster when their substrate is present. [ Nature vol. 517 pp. 149 – 150, 227 – 230 ’15 ] The hydrolysis of urea by urease and the conversion of H2O2 to O2 and water by catalase enhances the molecular diffusion of the enzymes (this is called anomlous diffusion).If you inhibit catalase enzymatic activity using azide the anomalous diffusion disappears (even though there’s still plenty of H2O2 around). This work also showed that the rate of diffusion of catalase, urease and 2 more ezymes correlates with the heat produced by the reaction catalyzed.

Heating the catalytic center of catalase (using a short laser pulse) produces the same anomalous diffusion. Proteins exist in a world in which Brownian motion is governed by viscous forces rather than by inertia, so coasting (a la Galileo and Newton’s law of inertia) isn’t an option — continuous force generation is required.

Heat generated from each catalytic cycle could be transmitted through the enzyme as a pressure wave. For this to happen the catalytic center must be NOT at the center of mass of the enzyme, so the pressure wave will create differential stress at the enzyme solvent interface (which should propel the enzyme). They call this the chemoacoustic effect.

Molecular dynamics simulations suggest that the transmission of energy through a protein can be quite fast (5 Angstroms/picoSecond) and nonuniformly distributed.

Some enzymes have a near perfect catalytic efficiency. Every time a substrate hits them, the substrate is converted to product. Examples include catalase, acetyl cholinesterase, fumarase, and carbonic anhydrase. There are 100 million to a billion collisions per mole per second in solution.

Could this be a product of evolution (to make enzymes actively search out substrates?). Note, this won’t work if the catalytic center of the enzyme is in the center of mass.

I doubt that much catalytic efficiency is gained by having a huge protein molecule sluggishly move through the cytoplasm. Why? The molecular mass of H2O2 is 19 Daltons (vs. 18 for water), so it moves slightly more slowly but water moves at 20C in water at 590 meters/second. Of course it doesn’t get very far before it bumps into another water molecule and gets deflected.

Is there an ace physical chemist out there who can put numbers on this. I couldn’t believe that I couldn’t find a simple expression for the relation between the diffusion coefficient and the mass of the diffuser, ditto for the atomic volume of a water molecule, although I’m guessing that it’s pretty close to the length of the H – O bond (.95 Angstroms) giving a mass of 3.6 cubic Angstroms. I wanted this so I could see how much room to roam a water molecule has.

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Comments

  • DN  On January 12, 2015 at 8:57 pm

    Wouldn’t the enzymes run away? They would bog down in low concentration areas.

    The effect might have some evolutionary significance for immunity, by making catalase flee from sites where immune cells are trying to oxidize bacteria to death. Even if it were physically small, it does not take much to help an immune cell a long way from a capillary trying to get ahead of an exponential growth curve.

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