Interactions of recombinant N-lobe of human serum transferrin (hTF/2N) with Bi3+, a metal ion widely used in medicine, have been investigated by both UV and NMR spectroscopy. The bicarbonate-independent stability constant for Bi3+ binding (K*) to hTF/2N was determined to be log K* 18.9±0.2 in 5 mM bicarbonate/10 mM Hepes buffer at 310 K, pH 7.4. The presence of Fe3+ in the C-lobe of intact hTF perturbed Bi3+ binding to the N-lobe, whereas binding of Bi3+ to the C-lobe was unaffected by the presence of Fe3+ in the N-lobe. Reactions of Bi3+ (as bismuth nitrilotriacetate or ranitidine bismuth citrate) with hTF/2N in solutions containing 10 mM bicarbonate induced specific changes to high-field 1H-NMR peaks. The 1H co-ordination shifts induced by Bi3+ were similar to those induced by Fe3+ and Ga3+, suggesting that Bi3+ binding causes similar structural changes to those induced by hTF/2N. 13C-NMR data showed that carbonate binds to hTF/2N concomitantly with Bi3+.
N-lobe versus C-lobe complexation of bismuth by human transferrin
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Hongzhe SUN, Hongyan LI, Anne B. MASON, Robert C. WOODWORTH, Peter J. SADLER; N-lobe versus C-lobe complexation of bismuth by human transferrin. Biochem J 1 January 1999; 337 (1): 105–111. doi: https://doi.org/10.1042/bj3370105
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