Comparative studies on salivary kallikrein from cystic fibrosis patients and controls

Kallikrein (EC 3.4.21.8) has been purified from the saliva of cystic fibrosis (CF) patients and from healthy individuals. The yields of enzyme are the same for both kinds of saliva. The CF and normal kallikrein have similar physical-chemical properties, such as amino acid composition, electrophoretic mobilities in polyacrylamide gels when different conditions are used, intrinsic fluorescence, and circular dichroism. The enzymes have no alpha-helix structure but large amounts of pleated sheet structure. CF and normal salivary kallikrein have also similar enzymatic properties, for example both enzymes show maximum activity at pH 8.2. An identical value of Km = 0.4 mM has been found for both enzymes with N-benzoyl arginine ethyl ester as substrate, despite the fact that the kallikreins are inhibited by high substrate concentrations. The results of this investigation show that the salivary kallikrein in CF is normal and that it has normal activity. This leads us to suggest that the salivary kallikrein is not the cause of the observed abnormalities in CF saliva.