Iodination of Ricin D

Abstract

Approximately five tyrosine residues of ricin D were iodinated preferentially under appropriate conditions probably forming diiodotyrosine. Iodination of this toxin carried out in 0.1M phosphate buffer at pH 7.0 and 0°C for 60min with a 20 fold molar excess of iodine per mole of protein, yielded a main component which appeared as a single band on polyacrylamide gel disc electrophoresis. Analysis of protein-bound radioactivity and the content of diiodotyrosine of ¹³¹I-labeled ricin D revealed that two tyrosine residues in the isoleucyl chain and three in the alanyl chain were substituted. The toxicity of iodinated ricin D decreased to one hundredth of that of native protein. However, the hemagglutinating activity of this protein was not affected by the iodination reaction.