Spectroscopic and thermodynamic studies on the binding of gadolinium(III) to human serum transferrin

Journal Article · Tue Feb 09 04:00:00 EST 1988 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00403a033· OSTI ID:5408639

Zak, O; Aisen, P

A wide variety of thermodynamic, kinetic, and spectroscopic studies have demonstrated differences between the two metal-binding sites of transferrin. In the present investigation, the authors have further assessed these differences with respect to the binding of gadolinium, evaluated by UV difference spectrophotometry, electron paramagnetic resonance (EPR) titration, EPR difference spectroscopy in conjunction with urea gel electrophoresis, and equilibrium dialysis. Combinations of these studies establish that only one site of the protein binds Gd(III) sufficiently firmly to be characterized. In order to reveal which of the two sites accepts Gd(III), we made use of monoferric transferrins preferentially loaded with Fe(III) at either site in EPR spectroscopic studies. Because of the overlap of signals, difference spectroscopy was required to distinguish resonances arising from Fe(III) and Gd(III) specifically complexed to the protein. When iron is bound to the C-terminal site, leaving the N-terminal site free for binding of gadolinium, the difference spectrum shows no evidence of specific binding. However, when iron is bound to the N-terminal site, the difference spectrum shows a resonance line at g' = 4.1 indicative of specific binding, thus implicating the C-terminal site in the binding of Gd(III). The effective stability constant for the binding of Gd(III) to this site of transferrin at pH 7.4 and ambient pCO/sub 2/ is 6.8 x 10/sup 6/ M/sup -1/. At physiological pCO/sub 2/, the formation of nonbinding carbonato complexes of Gd(III) precludes a substantial role from transferrin in the transport of the lanthanide in vivo.

• Research Organization: Albert Einstein College of Medicine, Bronx, NY (USA)
• OSTI ID: 5408639
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:3; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
ANIMALS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BLOOD SERUM
COMPLEXES
CONFIGURATION INTERACTION
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
ELECTRON SPECTRA
ELECTRON SPIN RESONANCE
ELECTROPHORESIS
EVEN-ODD NUCLEI
GADOLINIUM 153
GADOLINIUM COMPLEXES
GADOLINIUM ISOTOPES
GLOBULINS
GLOBULINS-BETA
INTERMEDIATE MASS NUCLEI
IRON COMPOUNDS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
MAGNETIC RESONANCE
MAMMALS
MAN
METALLOPROTEINS
NUCLEI
ORGANIC COMPOUNDS
PRIMATES
PROTEINS
RADIOISOTOPES
RARE EARTH COMPLEXES
RARE EARTH ISOTOPES
RARE EARTH NUCLEI
REACTION KINETICS
RESONANCE
SPECTRA
SPECTROPHOTOMETRY
TRANSFERRIN
TRANSITION ELEMENT COMPOUNDS
ULTRAVIOLET SPECTRA
VERTEBRATES