On the inhibition of human leukocyte elastase by trifluoroacetyl tripeptides

The recently reported Ki values for human leukocyte elastase and a series of trifluoroacetylated peptides are erroneous because the enzyme preparation was contaminated by a small amount of porcine pancreatic elastase. The correct Ki values are much higher. However, trifluoroacetylated peptides are still much more potent inhibitors than the corresponding acetylated peptides.