Protein a from Staphylococcus Aureus

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Abstract
Protein A from the cell walls of Staphylococcus aureus reacts with the Fc part of certain immunoglobulins from several species. Tetranitromethane has been used for the quantitative nitration of the four tyrosyl residues in protein A. The nitrotyrosines formed were subsequently reduced to the corresponding amino-tyrosyl groups with sodium dithionite. After nitration, protein A lost almost completely its original reactivity towards the Fc fragments of IgG while amino-protein A retained about 40% of its activity, as estimated by quantitative single immunodiffusion tests against normal dog serum. The activity towards rabbit anti-protein A serum was not changed, while neither nitro protein A nor amino protein A agglutinated sensitized sheep red blood cells. The significance of the tyrosines in the active sites of protein A is discussed.

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