The selective degradation of injected proteins occurs principally in the cytosol rather than in lysosomes

Cell. 1981 Jul;25(1):83-93. doi: 10.1016/0092-8674(81)90233-6.


These studies use microinjection to determine whether the selective degradation of cytosolic proteins involves selective transfer of proteins to lysosomes or selective proteolysis within the cytosol. 14C-Sucrose-labeled bovine serum albumin (14C-sucBSA) was conjugated to polylysine, and monolayers of L929 cells were exposed to the conjugate. The 14C-sucrose-labeled peptides that arose upon degradation of the added 14C-sucBSA polylysine accumulated exclusively within lysosomes. In contrast, when 14C-sucBSA or 14C-sucrose-labeled pyruvate kinase (14C-sucPK) was microinjected into L929 cells, over half the 14C-sucrose-labeled peptides derived form the injected proteins were present in the postlysosomal supernatant. Control experiments demonstrated that the microinjection procedure did not cause 14C-sucrose peptides to leak from lysosomes. Therefore, the presence in the cytosol of substantial amounts of the degradation products from injected 14C-sucBSA and 14C-sucPK confirms the existence of a major proteolytic system(s) within or readily accessible to the cytosol of animal cells.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cell Line
  • Cytosol / metabolism*
  • Humans
  • Kinetics
  • L Cells
  • Lysosomes / metabolism*
  • Mice
  • Microinjections
  • Proteins / metabolism*
  • Pyruvate Kinase / metabolism
  • Serum Albumin, Bovine / metabolism
  • Sucrose


  • Proteins
  • Serum Albumin, Bovine
  • Sucrose
  • Pyruvate Kinase