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.