Iodination of a tyrosyl residue in staphylococcal α-toxin

Abstract

Iodination of staphylococcal .alpha.-toxin by the lactoperoxidase method resulted in the maximal incorporation of .apprx. 2.5 I atoms/molecule of .alpha.-toxin. The iodination primarily involved a single tyrosine residue as shown by analysis of CNBr and tryptic peptides. Iodination at a level of 1.2 I atoms/.alpha.-toxin molecule led to a dramatic decrease in the hemolytic and lethal activities, although no decrease in the binding of iodinated toxin to rabbit erythrocytes was observed. Monoiodinated .alpha.-toxin had 15% of the specific hemolytic activity of native .alpha.-toxin. Incubation of rabbit erythrocytes with iodinated .alpha.-toxin led to a significant protection from the hemolytic activity of native .alpha.-toxin added later. Modification of a single unique tyrosyl residue in .alpha.-toxin apparently permits the resolution of .alpha.-toxin''s biological activities from its cell binding activity. [The possible specific mode of action of the .alpha.-toxin is discussed.].