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  • Title: Interaction of inhibitin with the human erythrocyte Na+(Li+)i/Nao+ exchanger.
    Author: Morgan K, Spurlock G, Collins PA, Mir MA.
    Journal: Biochim Biophys Acta; 1989 Feb 13; 979(1):53-61. PubMed ID: 2917166.
    Abstract:
    The kinetic interactions of inhibitin, a peptide isolated from cultured leukaemic promyelocytes, with erythrocyte Na+/Na+ and Na+/Li+ exchanges have been investigated. Inhibitin (1 microM) reduced the ouabain- and bumetanide-resistant sodium efflux and influx by equivalent amounts indicating an inhibitin-sensitive exchange component of 0.52 mmol/l per h. This value was not significantly different from that measured as the difference in sodium-rich (140 mM) and sodium-free media (0.49 mmol/l per h). Similarly, the inhibitin-sensitive lithium efflux was equivalent to the sodium/lithium countertransport component (0.36 vs. 0.34 mmol/l per h), indicating that both exchanges were mediated by the same transport process, which is inhibitin-sensitive. The dose-response curve revealed the presence of a single inhibitin binding site per exchanger with a Ki of 2.10(-7) M. In kinetic inhibition studies, inhibitin (0.1 microM) decreased the Vmax of ouabain- and bumetanide-resistant sodium efflux with no effect on the Km for external sodium, i.e., inhibitin displayed a non-competitive mechanism of action. These findings indicate that inhibitin interacts with the Na+(Li+)i/Nao+ exchanger at a site distinct from the sodium binding site.
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