Summary
The enzyme that fixes carbon dioxide in the Calvin cycle and is likely the most abundant protein on Earth.
In depth
It is slow (3 to 10 reactions per second) and makes mistakes by binding O2. Plants make large amounts to compensate, making up about 50 percent of leaf protein. It is a target for improving crop yields.
Rubisco's slow rate and confusion with oxygen suggest that it evolved when oxygen was scarce. Plants compensate by making lots of it, and by concentrating CO2 in C4 and CAM plants.
Remember: rubisco is in the stroma and is made of large and small subunits.
Rubisco (ribulose bisphosphate carboxylase/oxygenase) is the most abundant protein on Earth, with about 16 subunits (8 large encoded in the chloroplast and 8 small in the nucleus). Its poor specificity probably reflects evolution in an ancient atmosphere with high CO2 and low O2. At higher temperatures, oxygenation increases, causing photorespiration and losing up to 25 percent of fixed carbon in C3 plants.
Engineering efforts include improving the enzyme, adding carbon-concentrating mechanisms such as cyanobacterial carboxysomes, and moving C4 traits into rice. Rubisco is also a source of protein for food, extracted from leaves.
Frequently asked questions
What is Rubisco?
The enzyme that fixes carbon dioxide in the Calvin cycle and is likely the most abundant protein on Earth.
Which area of biology covers Rubisco, and how advanced is it?
Rubisco is one of the 56 topics in Plant Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Photosynthesis Efficiency Engineering, Photorespiration, C4 Photosynthesis.
Why does Rubisco matter?
Raising rubisco efficiency is a key target for increasing crop yields.
Can you give an example of Rubisco?
The enzyme is estimated to be the most abundant on Earth.
What should I learn before Rubisco?
Work through the Beginner topics in Plant Biology first, such as Plant Kingdom, Photosynthesis, Chlorophyll, then return to Rubisco. Intermediate topics assume the Beginner vocabulary.
What topics are related to Rubisco?
The closest topics to Rubisco are Photosynthesis Efficiency Engineering, Photorespiration, C4 Photosynthesis, Photosynthesis. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Rubisco?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Rubisco. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Rubisco different from Photosynthesis Efficiency Engineering?
Rubisco: The enzyme that fixes carbon dioxide in the Calvin cycle and is likely the most abundant protein on Earth. Photosynthesis Efficiency Engineering: Strategies include improving rubisco, adding carbon concentrating mechanisms and optimising canopy light use. Read both side by side and note what each one explains.
How should I study Rubisco step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Photosynthesis Efficiency Engineering and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.