What Is the Most Abundant Protein?

Have you ever wondered what the most abundant protein is? The answer depends on whether you want to know the most common protein in the world, in your body or in a cell.

Protein Basics

A protein is a polypeptide, a molecular chain of amino acids. Polypeptides are, indeed, the building blocks of your body. And, the most abundant protein in your body is collagen. However, the world's most abundant protein is RuBisCO, an enzyme that catalyzes the first step in carbon fixation.

Most Abundant on Earth

RuBisCO, whose full scientific name is "ribulose-1,5-bisphosphate carboxylase/oxygenase," according to Study.com, is found in plants, algae, cyanobacteria, and certain other bacteria. Carbon fixation is the main chemical reaction responsible for inorganic carbon entering the biosphere. "In plants, this is part of photosynthesis, in which carbon dioxide is made into glucose," notes Study.com.

Since every plant uses RuBisCO, it is the most plentiful protein on earth with nearly 90 million pounds produced every second, says Study.com, adding that it has four forms:

• Form I, the most common type is found in plants, algae, and some bacteria.
• Form II is found in different types of bacteria.
• Form III is found in some archaea.
• Form IV is found in some bacteria and archaea.

Slow Acting

Surprisingly, each individual RuBisCO is not all that efficient, notes PBD-101. The website, whose full name is "Protein Data Bank," is coordinated by Rutgers University, the University of California, San Diego, and San Diego State University as a study guide for college students.

"As enzymes go, it is painfully slow," says PBD-101. Typical enzymes can process a thousand molecules per second, but RuBisCO fixes only about three carbon dioxide molecules per second. Plant cells compensate for this slow rate by building lots of the enzyme. Chloroplasts are filled with RuBisCO, which comprises half of the protein. "This makes RuBisCO the most plentiful single enzyme on the Earth."

In the Human Body

Around 25 percent to 35 percent of protein in your body is collagen. It is the most common protein in other mammals, too. Collagen forms connective tissue. It is found primarily in fibrous tissue, such as tendons, ligaments, and skin. Collagen is a component of muscle, cartilage, bone, blood vessels, the cornea of your eye, intervertebral discs, and your intestinal tract.

It's a little harder to name a single protein as the most common in cells because the composition of cells depends on their function:

• Actin is a very common protein that is found in all eukaryotic cells.
• Tubulin is another important and abundant protein used in cellular division among other purposes.
• Histones, associated with DNA, are present in all cells.
• Ribosomal proteins are abundant since they are needed to produce other proteins.
• Red blood cells contain high concentrations of the protein hemoglobin, while muscle cells contain a high level of the protein myosin.