<p>Have you ever wondered what the most abundant <a href="http://chemistry.about.com/od/chemistryglossary/a/proteindef.htm" data-component="link" data-source="inlineLink" data-type="externalLink" data-ordinal="1" rel="nofollow">protein</a> is? The answer depends on whether you want to know the most common protein in the world, in your body or in a cell.</p><h3>Most Abundant Protein in the World</h3>The most abundant protein in the world is <a href="http://chemistry.about.com/od/chemistryglossary/g/Rubisco-Definition.htm" data-component="link" data-source="inlineLink" data-type="externalLink" data-ordinal="2" rel="nofollow">RuBisCO</a>, which is an enzyme that catalyzes the first step in carbon fixation. RuBisCO 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.<h3>Most Abundant Protein in the Human Body</h3>The most abundant protein in your body is <a href="https://www.thoughtco.com/collagen-facts-and-functions-608923" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="3">collagen</a>. Around 25% to 35% 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 the eye, intervertebral discs and the intestinal tract.<h3>Most Common Protein in Cells</h3>It&#39;s a little harder to name a single protein as the most common protein in cells because the protein composition of cells depends on their function. Actin is a very common &#34;housekeeping&#34; 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 expressed in all cells. Ribosomal proteins are abundant, since they are needed to produce other proteins. The type of cell matters. Red blood cells contain high concentrations of the protein hemoglobin, while muscle cells contain high level of the protein myosin.