Alteration of infrared spectrum of serum transferrin by iron binding and lowered pH

Difference infrared spectra are reported for human serum transferrin in D2O as a function of iron binding or increased acidity. Spectral features dete cted as iron is bound at high pH include difference bands that are indicati ve of reduced solvent exposure and binding site ligation. More extensive sp ectral alterations, some of which indicate titration of carboxylic acid gro ups, are induced in the apo protein by lowering the pH in a manner consiste nt with that entailed in endocytosis. (C) 1999 John Wiley & Sons, Inc.