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EGG YOLK FACTOR OF STAPHYLOCOCCUS AUREUS I.

Nature of the Substrate and Enzyme Involved in the Egg Yolk Opacity Reaction

^a Department of Bacteriology, University of Wisconsin, Madison, Wisconsin

ABSTRACT

SHAH, D. B. (University of Wisconsin, Madison) AND J. B. WILSON. Egg yolk factor of Staphylococcus aureus. I. Nature of the substrate and enzyme involved in the egg yolk opacity reaction. J. Bacteriol. 85:516–521. 1963.—Some pathogenic staphylococci produce an opacity reaction when grown in media containing egg yolk. The egg yolk factor is a lipase with a requirement for a fatty acid acceptor, rather than any of the three lecithinases. Highest amounts of egg yolk factor were obtained in Heart Infusion broth rather than nutrient broth or Casman's synthetic medium. The lowest density lipo-protein (lipovitellenin) isolated by ultracentrifugation of egg yolk has been identified as the opacity-producing substrate. The lipase acts on the lipid moiety, resulting in alterations in the solubility of lipovitellenin. Lipolysis is optimal at pH 8. The optimal pH for the opacity reaction is at pH 5.5 and 8. The protein (vitellenin) in lipovitellenin has an isoelectric point at pH 5.5. It is proposed that slight alterations in the stabilizing lipid due to lipolysis and the very low solubility of vitellenin may drastically alter the solubility of lipovitellenin at pH 5.5.

¹ Present address: Johns Hopkins-LWM, School of Hygiene, Baltimore, Md.