STAPHYLOCOCCAL NEUTRAL PHOSPHATASE - A HIGHLY CATIONIC MOLECULE WITH BINDING-PROPERTIES FOR IMMUNOGLOBULIN

Staphylococcal neutral phosphatase (NPtase) was purified from two Stap hylococcus aureus strains by sequential high salt extraction, ultracen trifugation and ion exchange chromatography. The enzyme showed maximum phosphatase activity at neutral pH, appeared as two bands in SDS-PAGE (31 and 32 kDa), and the isoelectric point was > 10. No close similar ity between NPtase and other known bacterial proteins in respect of th eir N-terminal amino acid sequences was found. Purified NPtase bound r at and human polyclonal IgG [intact and F(ab')(2) fragments], IgM, IgA , intact myeloma immunoglobulins, myeloma light chains, gamma heavy ch ain and, with a much lower affinity, Fc fragments. Furthermore, NPtase can bind serum albumin. Heparin, a highly negatively charged molecule , significantly inhibited NPtase binding to immunoglobulins and HSA, b ut did not inhibit the binding of specific antibodies to NPtase; this indicates that charge interactions are important. The newly characteri zed staphylococcal phosphatase with binding properties for immunoglobu lin is an interesting bacterial protein that could be involved in post -infectious sequelae.