An enzyme's optimum fits the place it works
- The idea
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- Why
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The idea
“All of an organism's enzymes work best at its body's conditions, or at its habitat's.”
Human enzymes are often described as working best near pH 7 and 37 °C, so it seems fair to give every enzyme its organism's conditions. Many enzymes work somewhere very different.
The short version
The mistake: All of an organism's enzymes work best at its body's conditions, or at its habitat's.
What's actually true: Each enzyme's optimum matches the conditions where that enzyme acts, which can differ from the rest of the body or the habitat.
- pH changes the charges on an enzyme's R groups. Those charges help hold the active site in shape, so each enzyme has a pH range where it works best.
- Your body holds many pH environments. The stomach is near pH 2 and the inside of a lysosome near 5, while blood stays near 7.4.
- Natural selection tunes each enzyme to the place where it acts. A lysosomal enzyme that leaks into the cytosol, near pH 7.2, barely works, which helps protect the cell.
- Microbes work the same way. Enzymes they release fit the water outside. Enzymes in their cytoplasm fit the pH the cell holds inside.
On the exam: Ask where the enzyme does its job. Its optimum matches that place, which may differ from the body or habitat.