Protein homeostasis, proteostasis, is essential to understand cell function. 
Protein degradation is a crucial component of the proteostatic mechanisms of the 
cell. Experiments on protein degradation are nowadays present in many 
investigations in the field of molecular and cell biology. In the present paper, 
we focus on the different experimental approaches to study protein degradation 
and present a critical appraisal of the results derived from steady-state and 
kinetic experiments using detection of unlabelled and labelled protein 
methodologies with a proteostatic perspective. This perspective allows 
pinpointing the limitations in interpretation of results and the need of further 
experiments and/or controls to establish "definitive evidence" for the role of 
protein degradation in the proteostasis of a given protein or the entire 
proteome. We also provide a spreadsheet for simple calculations of mRNA and 
protein decays for mimicking different experimental conditions and a checklist 
for the analysis of experiments dealing with protein degradation studies that 
may be useful for researchers interested in the area of protein turnover.