The elastase activity of alveolar macrophages: measurements using synthetic substrates and elastin.

Hamster, rat, guinea pig, and rabbit alveolar macrophage extracts were tested for elastase activity using elastin suspended in agar and two synthetic substrates, p-nitrophenyl N-tert-butyloxycarbonyl L-alaninate (NBA) and succinyl-L-alanyl-L-alanyl-L-alanine-p-nitroanilide (SLAPN). Activity against NBA was easily detectable, but there was no activity against SLAPN or against elastin-agar, although the assay procedures employing these substrates measured as little as 50 and 2 ng of pancreatic elastase, respectively. We concluded that unstimulated alveolar macrophages from these animals do not contain elastase, and that NBA activity is misleading as an indicator of elastolytic activity in crude alveolar macrophage extracts from these species.