The Formation of Diiodotyrosine in Iodinated Human Serum Albumin

Human serum albumin (HSA) has been allowed to react with varying amounts of iodine under mild conditions. Almost all of the tyrosyl residues of HSA may be converted to iodotyrosyl residues (primarily diiodotyrosyl) without producing significant changes in the conformation of the protein. Difference spectral measurements in urea show the disappearance of buried tyrosyl and the appearance of buried diiodotyrosyl residues; a difference spectral peak attributed to diiodotyrosyl residues in iodinated HSA is seen at 302 mµ. It is proposed that the partly nonaqueous environment of buried tyrosyl residues directs their preferential conversion to diiodotyrosyl residues.