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Subcellular localization of dipeptidyl peptidases II and IV in rat and rabbit alveolar macrophages
Abstract:
Pulmonary alveolar macrophages, obtained from healthy adult rats and rabbits by lung lavage, were evaluated for the presence of two serine exopeptidases having affinity for penultimate prolyl residues. Dipeptidyl peptidase II was visualized using either lysyl-prolyl or lysyl-alanyl derivatives of 4-methoxy-2-naphthylamine (MNA) as synthetic substrates at pH 5.5 and employing the osmiophilic coupler hexazotized pararosanaline (HXP) for localization. Reaction product was observed in 50-90% of alveolar macrophages and was confined principally to lysosomal structures. Interestingly, not all lysosomes reacted, suggesting that they have a variable but distinct degree of heterogeneity for this protease. Dipeptidyl peptidase IV was localized using glycyl-prolyl-MNA at pH 7.3 and HXP. Reaction product was observed exclusively on the external surface of the plasma membrane of the rat only. Its intensity appeared to be greater along the outer edge of what might be interpreted as the cell's glycocalyx. These proteases, by their localization and known substrate specificity, would be expected to make a significant contribution to the alveolar macrophage's proteolytic capabilities.
Insights
Pulmonary alveolar macrophages contain dipeptidyl peptidase II in lysosomes and dipeptidyl peptidase IV on the plasma membrane. These enzymes contribute to the macrophage
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Pulmonary alveolar macrophages are key immune cells in the lungs.
- Understanding their enzymatic machinery is crucial for lung immunity research.
- Serine exopeptidases with affinity for prolyl residues play roles in cellular processes.
Purpose of the Study:
- To investigate the presence and localization of two specific serine exopeptidases in pulmonary alveolar macrophages.
- To characterize dipeptidyl peptidase II and dipeptidyl peptidase IV within these cells.
- To assess the contribution of these proteases to alveolar macrophage proteolytic functions.
Main Methods:
- Pulmonary alveolar macrophages were isolated from healthy adult rats and rabbits via lung lavage.
- Dipeptidyl peptidase II was visualized using lysyl-prolyl/lysyl-alanyl-MNA substrates at pH 5.5 with hexazotized pararosanaline (HXP).
- Dipeptidyl peptidase IV was localized using glycyl-prolyl-MNA at pH 7.3 with HXP.
Main Results:
- Dipeptidyl peptidase II was found in 50-90% of alveolar macrophages, primarily within lysosomal structures, indicating lysosomal heterogeneity.
- Dipeptidyl peptidase IV was exclusively detected on the external surface of rat alveolar macrophage plasma membranes, potentially associated with the glycocalyx.
- Both enzymes exhibit substrate specificities suggesting significant roles in macrophage proteolytic activity.
Conclusions:
- Pulmonary alveolar macrophages possess distinct intracellular and cell surface serine exopeptidases.
- Dipeptidyl peptidase II is localized to lysosomes, while dipeptidyl peptidase IV is found on the plasma membrane in rats.
- These enzymes are likely important contributors to the overall proteolytic capacity of alveolar macrophages.