Protease activities in human tears.

Several protease activities were measured in human tears by six specific substrates. The specific activity of cathepsin B-like enzyme was 7-fold higher in Orientals than in Caucasians. The trypsin-like and cathepsin C-like enzyme activities also showed 3 to 4-fold higher in Orientals than in Caucasians. However, the deviation in the activities of these two enzymes was high in both Orientals and Caucasians. Similar results were obtained when comparing the protease activities of tear collected by glass capillary and a filter-paper strip method. Since a surface-active small molecular weight fraction can be produced by incubation of freshly collected tears for 4 hours at 37 degrees C, the low molecular weight surfactant may be a proteolytic product.