Chemical modifications of the tryptophan groups of transferrin.

Abstract

The tryptophan contents of human serum transferrin and human lactotransferrin have been estimated by colorimetric and spectrophotometric procedures. The nine tryptophan residues of human serum transferrin have been modified by 2‐nitrophenylsulphenyl chloride in 30% acetic acid, 2‐hydroxy‐5‐nitrobenzyl bromide at pH 3 and dimethyl‐(2‐hydroxy‐5‐nitrobenzyl)‐sulphonium bromide at pH 7.6. Upon modification under acidic conditions the iron‐binding capacity falls off linearly with degree of modification. At pH 7.6 no fall off in iron‐binding capacity was observed with a maximum of 8.4 2‐hydroxy‐5‐nitrobenzyl residues bound per molecule of transferrin. The results have been interpreted as showing that tryptophan residues are not directly involved in the iron‐binding sites of transferrin.