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Degradation of horseradish peroxidase after microinjection into mammalian cells
S E Knowles1, M F Hopgood, F J Ballard
1CSIRO (Australia) Division of Human Nutrition, Adelaide.
Abstract:
Horseradish peroxidase (HRP) has been microinjected into mammalian cells in tissue culture by the erythrocyte ghost-mediated technique. This protein was selected because it can be localized and quantified after injection by cytochemical and spectrophotometric methods. HRP labeled by reductive methylation retained full catalytic activity, was efficiently loaded into erythrocyte ghosts, and did not associate to a significant degree with ghost membranes. A combination of cytochemical staining and autoradiography established that HRP injected into rat L6 myoblasts, HE(39)L human diploid fibroblasts, or HeLa cells was intracellular and uniformly distributed throughout the cell, while cell lysis techniques showed that the catalytically active HRP was not membrane bound. Inactivation of labeled HRP after injection paralleled the disappearance of the 40-kDa polypeptide, and was always more rapid than its overall degradation. This difference was associated with a pool of water-insoluble radioactivity in the injected cells. This material was of smaller molecular size than the native protein: many labeled peptides were detected in the range of 10 to 38 kDa. By the use of inhibitors of autophagic proteolysis or lysosomal function it was established that HRP degradation was not subjected quantitatively to the same regulatory processes as the average endogenous protein labeled in the same cultures.
Insights
Horseradish peroxidase (HRP) was microinjected into mammalian cells using the erythrocyte ghost technique. The study found that injected HRP is intracellular and degrades via a unique pathway, distinct from endogenous protein degradation.
Area of Science:
- Cell Biology
- Biochemistry
- Protein Degradation
Background:
- Horseradish peroxidase (HRP) is a valuable enzyme for cellular studies.
- Microinjection techniques allow direct introduction of molecules into cells.
- Understanding protein fate within cells is crucial for biological research.
Purpose of the Study:
- To investigate the intracellular fate and degradation of microinjected Horseradish peroxidase (HRP) in mammalian cells.
- To determine if HRP degradation follows the same pathways as endogenous proteins.
- To characterize the molecular changes of HRP post-injection.
Main Methods:
- Microinjection of HRP into mammalian cell lines (rat L6 myoblasts, human diploid fibroblasts HE(39)L, HeLa cells) using the erythrocyte ghost-mediated technique.
- Cytochemical staining and autoradiography for HRP localization and quantification.
- Cell lysis and spectrophotometric assays to assess HRP activity and membrane association.
- Analysis of HRP degradation products using molecular weight determination.
- Inhibition studies targeting autophagic proteolysis and lysosomal function.
Main Results:
- Microinjected HRP was found to be intracellular and uniformly distributed in all cell types tested.
- Catalytically active HRP was not associated with cell membranes.
- HRP inactivation preceded overall degradation, with evidence of water-insoluble, smaller molecular weight labeled peptides.
- HRP degradation was not quantitatively regulated by the same processes as endogenous proteins.
Conclusions:
- The erythrocyte ghost-mediated microinjection is an effective method for introducing functional HRP into mammalian cells.
- Injected HRP undergoes intracellular degradation through a pathway that differs from the typical degradation of endogenous proteins.
- The findings suggest specific regulatory mechanisms govern the degradation of exogenous proteins within the cell.