PASS Scripta Varia 21 - Pontifical Academy of Sciences

INTRACELLULAR PROTEIN DEGRADATION
Figure 1. The lysosome: Ultrathin cryosection of a rat PC12 cell that had been loaded for 1 hour
with bovine serum albumin (BSA)-gold (5 nm particles) and immunolabelled for the lysosomal
enzyme cathepsin B (10-nm particles) and the lysosomal membrane protein LAMP1 (15 nm particles).
Lysosomes are recognized also by their typical dense content and multiple internal membranes.
Bar, 100 nm. Courtesy of Viola Oorschot and Judith Klumperman, Department of Cell
Biology, University Medical Centre Utrecht, The Netherlands.
of endogenous proteins and cellular organelles (which are targeted by microand
macro-autophagy; see Figure 2, p. 372). The lysosomal/vacuolar system
as we currently recognize it is a discontinuous and heterogeneous digestive
system that also includes structures that are devoid of hydrolases – for example,
early endosomes which contain endocytosed receptor-ligand complexes and
The Scientific Legacy of the 20 th Century
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