Protein turnover refers to the biological process that breaks down protein within the cell. Human and animal cells rely on protein in order to divide, multiply and grow. In order to use protein, cells constantly work at synthesizing and degrading it.
Whether a cell is bringing protein molecules together or breaking them apart, the process is considered to be protein turnover. Essentially, the body is processing a certain amount of protein within a specified time frame. Protein does not usually remain stagnant once it enters the body, although some forms may last longer than others.
Organs within the body rely on protein turnover in order to regenerate tissue. Muscles use the process to repair and strengthen themselves. When protein is ingested through food sources, the cells are able to isolate and break down the protein. Any unused and excess protein may be eliminated from the body.
Even cells that are not in a reproduction or growth stage participate in the protein turnover process. These cells still need the nutrient in order to maintain stability and survive. Some forms of protein are digested and broken down rather quickly to ensure this happens. Changes within the body or the type of environment it encounters can speed up turnover.
There are a few factors that might affect the body's ability to break down and synthesize protein. One of those factors is free radicals that result from the oxidation process. When cells are exposed to oxygen, it creates free radicals that can also lead to oxidized amino acid residues. Certain types of amino acids or proteins, such as lysine, are more vulnerable to oxidation.
Other types of proteins tend to live under two hours, due to their composition. Proteins that are comprised of components such as serine and glutamate generally get digested first. Sometimes referred to as a PEST sequence, proteins that contain certain terminal components are often broken down first since they tend to be more susceptible and vulnerable. N-terminal proteins are another type of amino acid that break down rather quickly.
During the protein turnover process cells tend to take advantage of protein types that have undergone some sort of chemical transformation. Modified or mutant proteins are more vulnerable to being broken down. Certain types of proteins and enzymes are processed for specific functions, such as blood clotting, cellular responses to stress, and DNA expression.