The specificity of macrophage elastase obtained from mouse peritoneal exudative macrophages was determined in the hydrolysis of the oxidized insulin B-chain. This elastase hydrolysed two bonds, namely Ala-Leu and Tyr-Leu. The rate of hydrolysis of the latter was two to three times greater than that of the former. The hexapeptide Glu-Ala-Leu-Tyr-Leu-Val, obtained by cleavage of the insulin B-chain, was not hydrolysed by macrophage elastase. When EDTA was present, proteolysis of the B-chain was not observed. The macrophage elastase is therefore different from the neutrophil elastase in specificity and mechanism.
