Measuring protein breakdown rate in individual proteins in vivo.

PURPOSE OF REVIEW: To outline different approaches of how protein breakdown can be quantified and to present a new approach to determine the fractional breakdown rate of individual slow turnover proteins in vivo. RECENT
FINDINGS: None of the available methods for determining protein breakdown can be used to determine the breakdown rate of specific proteins and, therefore, do not keep up to the preceding methodological demands in physiological research. A newly developed approach to determine the fractional breakdown rate of single proteins seems promising. Its conceptual advantage is that the proteins of interest are the site of measurement. Hence, the application initially demands the proteins to be labeled with stable isotopically labeled amino acids. Subsequently, the loss of label from the proteins will be dependent on the protein breakdown rate when no labeled amino acids are reincorporated into the protein, the protein mass is steady, and when proteins contained in the measured fraction are stochastically selected for degradation.
SUMMARY: Although the synthesis rate of specific proteins can be accurately determined, methodological improvements are required to elucidate the physiological role of protein degradation. The novel approach is promising but future studies are needed to address its wider applicability.