Cornea-damaging proteases of Serratia marcescens

Fractionation of the culture supernatant fluids of Serratia marcescens, strain BG, by ammonium sulfate precipitation, isoelectric focusing, ion-exchange chromatography, hydroxyapatite adsorption chromatography, and gel filtration failed to separate the rabbit cornea-damaging activity and the in vitro protease activity of the preparations. Two proteases having similar molecular weights (44,000), estimated by gel filtration, and isoelectric points of approximately 5.0 and 5.3 were obtained free of detectable amounts of other known extracellular serratia enzymes. Heating a mixture of the two proteases for 15 minutes at 60 degrees C. resulted in complete loss of protease and cornea-damaging activities. Production of protease and cornea-damaging activities was inhibited by ammonium sulfate. The results support the conclusion that extracellular proteases produced in vitro by S. marcescens can elicit rapid and extensive damage to the rabbit cornea.