Analysis of an antistaphylococcal serum alpha globulin

Previous studies in this laboratory have shown that normal human serum contains an alpha globulin possessing lethal and antirespiratory action for staphylococci. In this study further description of the antistaphylococcal macromolecule is presented. The antistaphylococcal protein was shown to be homogeneous by both isoelectric focusing in sucrose density gradients and sodium dodecyl sulfate electrophoresis. An analysis of the chemical composition of the antistaphylococcal serum protein indicated the alpha globulin to be a glycoprotein composed of 22.5% carbohydrate and 77.2% protein as determined by amino acid analysis. The total carbohydrates included 11.08% protein-bound hexoses. 0.86% hexosamines, 4.3% sialic acid and 6.3% fucose. The mean isoelectric point, determined by isoelectric focusing in the range pH 3-6, was 4.73. Molecular weight studies on Sephadex G-200 dextran gel columns calibrated with proteins and glycoproteins indicated the molecular weight of the antistaphylococcal macromolecule to be 55,000-74,000 daltons respectively. SDS-gel electrophoresis indicated the molecular weight of antistaphylococcal serum protein was 62,000. Thus the antistaphylococcal alpha globulin does not appear to be related to other known serum bactericidins.