And going and going and going…

Reader Nico has an interesting question on the subject of enzymes: do they ever quit? Which is to say, do they stop working at some point just naturally, run out of go-juice or something along those lines? Nico, I’m not an organic chemist but when’t the last time I let that stop me? I believe the answer is no. Enzymes are not living organisms, so as far as I know they don’t run out of energy or anything like that. They are organic molecules (proteins) that living organisms use to perform very specific chemical jobs, converting x molecule — but only x molecule — into molecules y and z if that makes sense.

I think of them as sort of free-floating puzzle pieces. They lock onto a specific molecule, break it, move on to the next molecule, break it and so on, over and over and over again until they either run out of “x” molecules to break or are themselves damaged. A great illustration of this principle can be observed with a starch-thickened custards like pastry cream. Human saliva abounds in a starch-busting (amylose-busting) enzyme called amylase. When that busting occurs on a large enough scale the gel that gives pastry cream its thick texture breaks down, and fast. Which is why pastry cream liquifies so quickly in the mouth. It’s also why, if you introduce some amylase into a quantity of pastry cream by say, double dipping with a spoon, you run the risk of turning the entire batch into a runny mess. Very interesting things, those enzymes. Thanks for the question, Nico!

5 thoughts on “And going and going and going…”

  1. It depends on the enzyme. To explain, first I’ll bore you with some introductory chemistry/biochemistry. In a chemical reaction we talk about reactants being converted to products. If you had an infinite amount of time (and accept certain oversimplifications, like how the universe might end first), all reactions would go to equilibrium where there is some ration of reactants and products. For some reactions like the breakdown of starch by amylase or the breakdown of proteins by proteases from raw pineapple or papaya the equilibrium lies far toward the direction of the products. In other cases the equilibrium is on the other side or more in the middle. It depends on the relative energies of the products and reactants. In the reaction that converts glucose to fructose to make HFCS, the equilibrium is at around 42% fructose/58% glucose.

    Enzymes are catalysts. That means that they don’t change the position of the equilibrium, they just help get to equilibrium faster. Often millions of times faster or more. They can “run out of fuel” in the sense of running out of substrates. They effectively stop when the reaction they are catalyzing reaches equilibrium. But no matter how long you wait or how much enzyme you use, the HFCS treated with glucose isomerase will never get to more than 42% fructose (there are other tricks to get higher).

    They can also stop if they are damaged, and there are lots of reactions where the active enzyme itself is a reactant and the product is a dead enzyme. Some enzymes, like the RNase that’s in your fingerprints, can survive boiling. Others seem to die if you look at them hard; those have frustrated many generations of biochemists.

    1. The most obvious example that comes to my mind is boiling an egg-it certainly doesn’t look much like the original egg, and the denaturation of the proteins is pretty much irreversible.

      Also, I think this is also related to an earlier post on why you poach the pears (to denature the enzymes that cause the browning)!

      1. Nice, Nemo. Thanks!

        And yes, no doubt. Enzymes have been a recurrent theme these last couple weeks!


        – Joe

  2. I actually learned that there had to be something in my saliva due to eating rice/tapioca pudding out of the container and sticking it back in the fridge. When you are the only one in the house that likes the texture, eating it out of the container just seems easier.
    And then, to hit home on that, making homemade pudding and taking a couple bites and putting it back in the fridge. (taste test!) Yeahhh… soup.

    1. Yep, enzymes. They’re hard working little things…and they work darn quickly too. Great comment, Kitty!


      – Joe

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