Fixing photosynthesis by engineering it to recycle a toxic mistake
And photosynthesis depends on an enzyme called RuBisCO, which uses carbon dioxide from the atmosphere to build sugars. So, by extension, RuBisCO may be the most important catalyst on the planet.
Unfortunately, RuBisCO is, well, terrible at its job. It might not be obvious based on the plant growth around us, but the enzyme is not especially efficient at catalyzing the carbon dioxide reaction. And, worse still, it often uses oxygen instead. This produces a useless byproduct that, if allowed to build up, will eventually shut down photosynthesis entirely.