Many factors trigger the degradation of proteins, including changes in 
environmental conditions, genetic mutations, and limitations in the availability 
of cofactors. Despite the importance for viability, still very little is known 
about protein degradation and its regulation. The degradation of the most 
abundant membrane protein on Earth, the light-harvesting complex of Photosystem 
II (LHC II), is highly regulated under different environmental conditions, e.g. 
light stress, to prevent photochemical damage of the reaction center. However, 
despite major effort to identify the protease/proteases involved in the 
degradation of the apoproteins of LHC II the molecular details of this important 
process remain obscure. LHC II belongs to the family of chlorophyll a/b binding 
proteins (CAB proteins) and is located in the thylakoid membrane of the plant 
chloroplast. The results of biochemical experiments to isolate and characterize 
the protease degrading LHC II are summarized here and compared to our own recent 
finding indicating that a metalloprotease of the FtsH family is involved in this 
process.