Effect of subunit size and conformation on the rate of lysosomal degradation of extracellular proteins in cultured mouse peritoneal macrophages.

The degradation of nine well-defined proteins was studied in cultured mouse peritoneal macrophages following their uptake by fluid phase pinocytosis. After uptake, approximately one-third of the radioactivity was released into the medium in the form of trichloroacetic acid/phosphotungstic acid-insoluble material. When the time courses for the appearance of trichloroacetic acid/phosphotungstic acid-soluble and -insoluble radioactivities were independently analyzed, identical observed rate constants (kobs) were obtained.

Degradation and regurgitation of extracellular proteins by cultured mouse peritoneal macrophages and baby hamster kidney fibroblasts. Kinetic evidence that the transfer of proteins to lysosomes is not irreversible.

The uptake and degradation of bovine serum albumin (BSA), bovine liver catalase, and rabbit muscle enolase have been studied in cultured mouse peritoneal macrophages (MPM) and baby hamster kidney fibroblasts (BHK cells). Rates constant for the uptake of the three proteins by MPM were similar. In addition, BSA accumulation was independent of BSA concentration in the uptake medium and was not inhibited by a large excess of serum, suggesting that protein accumulation was by fluid phase pinocytosis.