Abstract
Uteroferrin, a purple-colored, iron-containing glycoprotein, purified from the uterine fluid of progesterone-stimulated pigs, owes its natural purple color to a broad absorption band centered at 545 nm. Laser excitation within the visible absorption band of uteroferrin results in an intense resonance Raman spectrum which bears a striking resemblance to that reported for Fe(III)-transferrin, the iron transport protein of serum. Excitation profiles for the four resonance-enhanced bands of uteroferrin were obtained from 4579 A to 6741 A, using lines from Ar+ and Kr+ lasers. Each of the profiles have maxima near 545 nm. The spectral similarities of uteroferrin and Fe(III)-transferrin lead to the belief that the Fe(III) binding sites of the two proteins must be, at least in some respects, quite similar. In particular, it is concluded that, as in Fe(III)-transferrin, the metal binding site of uteroferrin contains a tyrosine ligand and that the visible absorption spectrum of uteroferrin results from a phenolate to Fe(III) charge transfer.
Highlights
Science und Uteroferrin, a purple-colored, iron-containing glycoprotein, purified from the uterine fluid of progesteronestimulated pigs, owes its natural purple color to a broad absorption band centered at 545 nm
Based upon the resonance Raman spectra of an Fe(III)-phenolate model compound, tyrosine was confidently identified as the iron ligand responsible for Fe(III)-transferrin’s intense visible absorption
It has been shown earlier that the ESR spectrum of uteroferrin is characteristic of high spin Fe(II1) in a rhombic field and, in that respect, is similar to spectra obtained from transferrin, ovotransferrin, and lactoferrin [7]
Summary
Laser excitation within the visible absorption band of uteroferrin results in an intense resonance Raman spectrum which bears a striking resemblance to that reported for. It is concluded that, as in Fe(III)-transferrin, the metal binding site of uteroferrin contains a tyrosine ligand and that the visible absorption spectrum of uteroferrin results from a phenolate to Fe(II1) charge transfer. Based upon the resonance Raman spectra of an Fe(III)-phenolate model compound, tyrosine was confidently identified as the iron ligand responsible for Fe(III)-transferrin’s intense visible absorption [10]. Conventional Raman scattering from a protein yields a complex spectrum composed of overlapping vibrational modes from the peptide backbone and amino acid side groups [9], excitation within the absorption band of a chromophoric protein.
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