Measuring levels of proteins by various technologies: can we learn more by measuring turnover?

In routine experiments, scientists measure the levels of various substances such as proteins after various treatments. Detection of a change in levels suggests an impact of treatment on that particular protein. However, we sometimes forget the importance of turnover in this process. Proteins have half-lives that may change in response to treatments (which is in fact why levels may change), and an examination of half-lives may yield better clues as to how treatment affects the protein. After an exploration of the quantitative aspects of protein turnover, several interesting conclusions may be drawn. (1) Even though levels of some proteins may NOT change after treatments, their half-lives and turnovers do change, and these may be more sensitive indicators of the impact of treatments on the proteins of interest. (2) Treatments can affect protein levels because they alter either the synthesis or degradation of the protein or both. But, the rate of change of the levels depends on the half-life of the protein. If the experimenter waits only a fraction of a half-life of the protein after treatment, no significant change in level may be found since it can take up to 5 half-lives for the protein level to adjust to about 97% of its new level after treatment. (3) Half-lives of the same protein can vary in different species and experimental conditions may have to be altered if using different species. These factors suggest that a consideration of protein turnover and half-lives will be useful for future studies of this type.