An expeditious and sensitive colorimetric method to measure elastase activity using Congo red-elastin as a substrate is described. Highly purified elastase EI as low as 1.65 μg may be assessed accurately within 1 h. This assay is thus 10-100 times more sensitive than previous methods using elastin as a substrate. In this assay method, however, the elastinolytic activity is amplified when a sufficient amount of trypsin and/or chymotrypsin is present in the assay samples. Therefore it is necessary to inhibit the activities of contaminant trypsin and/or chymotrypsin by limabean trypsin inhibitor (LBTI) and chymostatin, by which elastase activity was not influenced. And the coefficients between amidolytic and elastinolytic activities assayed by our methods of both highly purified and crude elastase preparations (AU/CU) were exactly equal to be about 14.
