What is the name of the most abundant protein on Earth?

Rubisco, or ribulose bisphosphate carboxylase/oxygenase, is recognized as the most abundant protein on Earth. This protein plays a critical role in photosynthesis, specifically in the Calvin cycle, where it catalyzes the conversion of carbon dioxide and ribulose bisphosphate into 3-phosphoglycerate, which is a precursor to glucose and other carbohydrates. Rubisco is found in all photosynthetic organisms, making it essential for plant growth and, consequently, for the entire food web.

In terms of abundance, rubisco is prevalent primarily because it is involved in the uptake of carbon dioxide from the atmosphere, a process that is fundamental to the growth of plant life. Since plants make up a significant portion of Earth's biomass, the accumulated presence of rubisco in these organisms leads to its classification as the most abundant protein globally.

While other proteins such as hemoglobin, actin, and collagen are important in their respective roles—transporting oxygen, providing structural support in cells, and serving as a key component of connective tissues—they do not match rubisco's ubiquity and abundance in nature.