What is the most abundant protein in the human body?
Collagen is the conventional whole-body answer by estimated protein mass. Actin often leads inside cells, hemoglobin in red cells, and albumin in plasma.
Collagen, especially type I collagen, is the conventional answer to the most abundant protein in the human body. That answer uses estimated total protein mass across all tissues.
Other answers use different denominators. Actin often leads inside eukaryotic cells, hemoglobin dominates red blood cells, and albumin is the most concentrated protein in plasma.
What is the most abundant protein in the human body?
Collagen is the conventional whole-body answer, and type I is the most abundant collagen.[1][2]
Collagen is a family of 28 proteins found mainly in the extracellular matrix, the material around cells that gives tissues structure. Collagens form much of the framework of skin, bone, tendons, ligaments, cartilage, blood vessels, and many organs.[1] This distribution is why collagen is usually named the body's most common protein by mass.
That ranking applies to the human body. Across the biosphere, Rubisco is the best-supported candidate for the most abundant protein on Earth.
“Most abundant” here refers to estimated total mass across the body. It does not mean the number of distinct protein sequences, protein-coding genes, or molecules in one cell. Those counting levels are separated in our guide to how many proteins there are.
Collagen is also not one sequence. Its alpha chains are distinct proteins that a sequence alignment compares separately, while whole-body estimates usually group the chains and collagen types under the single name “collagen.”
How much collagen is in the human body?
The often-repeated estimate is that collagen accounts for about 30% of total body protein, but no direct whole-human measurement establishes that share.[1][3]
A 70-kilogram reference-man model contains 10.5 kilograms of protein. Multiplying that estimate by 30% gives 3.15 kilograms, or about 7 pounds, of collagen.[6] This is a calculation from two reference values, not a measurement from one person. The 30% claim refers to protein mass, not total body weight.
A 2023 study traced the 30% claim through more than 50 papers and found no original whole-mammal measurement behind it. The researchers then measured entire mice using hydroxyproline, an amino acid enriched in collagen. Collagen accounted for about 12% of total protein in female mice and 17% in male mice.[3] Mouse results cannot be substituted for human values, but they show why 30% should be treated as an unverified human estimate.
Collagen abundance also changes sharply by tissue. The same study measured collagen at about 0.1% of protein in mouse brain and liver, around 3.5% in muscle and lung, 20% to 39% in skin, and 40% to 51% in tendon.[3]
The chart uses approximate values reported for four-week-old female CD1 mice. It compares the same denominator, collagen as a share of tissue protein, and should not be read as a set of human reference values.[3] Collagen's cross-linked fibers are difficult to dissolve and digest, so standard proteomics can undercount them.
What is the most abundant protein in a human cell?
No protein is most abundant in every human cell. Actin is the most abundant protein in most eukaryotic cells, but cell type, growth state, and whether abundance is measured by mass or molecule count can change the ranking.[11]
Actin forms the dynamic filaments that support cell shape, movement, division, and muscle contraction. Vertebrates express several closely related actin isoforms, including alpha actins in muscle and beta and gamma actins in other cells.[11] Calling actin the most abundant cellular protein describes a broad pattern, not a universal human-cell constant.
Red blood cells are the clearest exception. Each mature red blood cell contains about 270 million hemoglobin molecules, which account for roughly 90% of its dry weight.[5] A count of protein copies in a red blood cell will therefore name hemoglobin, not actin or collagen.
Copy number and protein mass also differ because protein molecular weights span a wide range. A protein can lead by molecule count without contributing the most mass across a tissue or the whole body.
Why are albumin and hemoglobin also called the most abundant protein?
Albumin is the most abundant protein in plasma, while hemoglobin dominates red blood cells and therefore the protein mass of whole blood.[4][5][10]
The Human Protein Atlas reports a mean albumin concentration of 40 grams per liter in plasma, and clinical laboratories commonly use a 60 to 80 gram-per-liter interval for total serum or plasma protein.[7][10] An adult has nearly 5 liters of blood, about 60% of which is plasma.[8] Multiplying 3 liters of plasma by 40 grams per liter gives about 120 grams of circulating albumin. This is a reference calculation, not a measurement from one person.
Adult hemoglobin reference ranges are about 130 to 170 grams per liter for men and 120 to 150 grams per liter for women.[9] Across 5 liters of blood, those concentrations correspond to roughly 600 to 850 grams of hemoglobin. This calculation includes hemoglobin inside red cells, whereas a plasma test excludes the cells.
| Scope | Most abundant protein | Basis |
|---|---|---|
| Whole body, by estimated protein mass | Collagen family, especially type I | Conventional answer; exact human share is unmeasured |
| Most eukaryotic cells | Actin | Cellular abundance; varies by cell type and method |
| Red blood cells | Hemoglobin | About 270 million molecules per cell and 90% of dry weight |
| Blood plasma | Albumin | About 40 g/L mean concentration in the Human Protein Atlas |
The comparison uses whole-body mass, cellular abundance, red-cell molecule count and dry mass, and plasma concentration. Those measures answer different questions and should not be ranked against one another as a single dataset.[1][2][5][10][11]
