Protein turnover refers to the degradation of proteins over time. It reflects the balance between a cells synthesis of protein and that proteins breakdown. This factor determines the concentration of a protein existing within a cell.
When there is a greater degree of protein synthesis than degradation occurring in an organism, it creates an anabolic state that generates lean tissue. The inverse is a catabolic state in which a greater degree of protein breakdown burns away lean tissues.
The aging process is believed to be connected to protein turnover and the build-up of damaged proteins within the body. Studies in protein turnover have shown some proteins to be short-lived, while others last much longer. The long-lived proteins are those which comprise the majority of proteins within a cell, while the short-lived ones are usually those associated with regulatory functions or abnormal proteins that are more prone to degradation.