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Contrasting Synergistic Anion Effects in Vanadium(V) Binding to Nicatransferrin versus Human Serum Transferrin

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journal contribution
posted on 15.12.2009, 00:00 by Jean P. Gaffney, Ann M. Valentine
Some ascidians sequester vanadium and other metal ions that are bound and transported in higher organisms by transferrin. The ascidian Ciona intestinalis has a monolobal transferrin (nicatransferrin) in its plasma. The binding of vanadium(V) to nicatransferrin was investigated by using isothermal titration calorimetry and UV−vis spectroscopy, in the presence and absence of NaHCO3, and was compared with human serum transferrin. Nicatransferrin and serum transferrin bind V(V) with similar strengths [K = (2.0 ± 0.6) × 105 M−1 for nicatransferrin]; however, nicatransferrin requires a synergistic anion for V(V) binding, whereas serum transferrin does not. Spectroscopy supports a different kind of coordination site.