Inhibition of human leucocyte elastase by polynucleotides

We have found that nanomolar range concentrations of transfer RNA inhibit human leucocyte elastase activity against synthetic or natural substrates. Titration curves give a stoichiometry of 9 +/- 1 elastase molecules inhibited per tRNA molecule. The interaction seems essentially electrostatic since similar inhibitions were measured with poly r(A) or calf thymus DNA, and because the increase in ionic strength leads to a decrease of inhibition. This observation appears to be specific of human leucocyte elastase since porcine pancreatic elastase, and both human and bovine chymotrypsins are not inhibited by tRNA.