The effect of extracellular proteases from gran-negative bacteria on the interaction of von Willebrand factor with human platelets.

FWPs are usually stable for several months. However, in less than a week, one lot of FWPs lost its ability to aggregate with bovine PAF or human vWF plus ristocetin. Initial experiments suggested that the loss of aggregability was caused by contamination of the FWPs with an extracellular protease of Serratia marcescens. Highly purified protease preparations from the culture filtrates of S. marcescens (SP), as well as from two strains of Pseudomonas aeruginosa, destroyed the aggregability of FWPs as a function of time and concentration. On the basis of azocasein units, the SP was found to be at least eight times more potent against FWPs as a substrate than either of the P. aeruginosa proteases. The effect of SP on FWP aggregability was inhibited by prior EDTA treatment and was restored by addition of Zn2+ in slight molar excess. Purified PAF, but not dilutions of bovine plasma, lost all PAF activity when incubated with SP. SP-treated FWPs would still aggregate with 10 microgram/ml polylysine. SP digestion of FWPs was more selective than digestion with trypsin or chymotrypsin, on the basis of both the polyacrylamide gel electrophoresis pattern and the amount of protein in the platelet digest supernatant. SP does not aggregate fresh washed platelets or initiate the release reaction but renders them unaggregable with vWF. SP and related proteases may be useful in the study of platelet membranes.