Bovine lens alpha-crystallin inhibited both porcine pancreatic elastase (PPE) and human neutrophil elastase (HNE), but not in the same manner. PPE was immediately inhibited with a stoichiometry of 10 moles of PPE inhibited per mole of alpha-crystallin. The inhibition was markedly decreased by the addition of even low levels of salts. The inhibition was transient, as PPE activity returned to normal with a t1/2 of 30 min even in low salt. HNE required a short preincubation to show maximum inhibition with a stoichiometry of approximately one mole of HNE inhibited per mole of alpha-crystallin. The inhibition of HNE was only slightly decreased by the addition of 0.1 M salt, and HNE activity returned slowly exhibiting a t1/2 of 30 hrs under these conditions. The inhibition of each enzyme by alpha-crystallin was evaluated by Dixon plots giving Ki values of 1.5 nM for PPE and 0.25 nM for HNE. DFP-trypsin was able to compete with PPE for binding to alpha-crystallin and cause the release of PPE already bound to alpha-crystallin. The inhibition of HNE, however, was unaffected by the addition of DFP-trypsin. A mixture of HNE and alpha-crystallin in 0.1 M NaCl was incubated at 25 degrees C for 6 hours. Aliquots showed a slow, continuous cleavage of the alpha-crystallin subunits by SDS-PAGE, but little or no increase in HNE activity.(ABSTRACT TRUNCATED AT 250 WORDS)