Purification of Staphylocidal β-Lysin from Rabbit Serum

A cationic protein of rabbit serum bactericidal for Staphylococcus aureus was purified. The specific activity per unit of protein of the purified staphylocidal preparation was approximately 37,000 times greater than that of the serum from which it was isolated. Similar techniques were used to purify serum beta-lysin active against Bacillus subtilis approximately 24,000 times. The staphylocidal activity cannot be attributed to the same beta-lysin active against B. subtilis, lysozyme, or antibody-complement systems. The concentrations of staphylocidal beta-lysin in the sera of the five mammalian species studied did not correlate with their beta-lysin activities against B. subtilis. The two beta-lysins are similar in that both were heat-stable, sensitive to trypsin digestion, had molecular weights near 6,000, and were found in higher concentrations in serum than in plasma. Furthermore, similar techniques can be used to absorb and elute both substances in highly purified forms using cellulose asbestos filter pads and ion exchange chromatography on carboxymethyl cellulose. In contrast to the beta-lysin against B. subtilis, the staphylocidal beta-lysin was not released from blood platelets, and it was inactive in the presence of heparin, sodium citrate, sodium oxalate, ethylenediaminetetraacetic acid, acidic phospholipids, and acid pH values. A variety of proteins, including those of normal serum, preferentially inhibited the bactericidal activity of staphylocidal beta-lysin but not the beta-lysin against B. subtilis.