NOTPME: a 31P NMR probe for measurement of divalent cations in biological systems.
1,4,7-Triazacyclononane-N,N',N''-tris(methylenephosphonate monoethylester) (NOTPME) has been synthesized, characterized and analyzed for use as a 31P NMR indicator of intracellular Mg2+ and Zn2+ ions. The 31P NMR spectrum of this chelate in the presence of metal ions shows characteristic resonances for the free chelate, Mg(NOTPME)-, Zn(NOTPME)-, and Ca(NOTPME)-. The Kd values indicate that this chelate has a 10-fold higher affinity for Mg2+ than for Ca2+ at physiological pH values. In the presence of Mg2+, NOTPME is readily loaded into red blood cells. A 31P NMR spectrum of red cells taken after several washings shows resonances characteristic of entrapped NOTPME and the Mg(NOTPME)- complex, the relative areas of which report an intracellular free Mg2+ concentration of 0.32 mM. The 31P chemical shifts of the free chelate and its metal complexes are far downfield from the typical phosphorus-containing metabolites observed in biological systems, thus making it possible to monitor intracellular cation concentrations and cell energetics simultaneously.
Ramasamy
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Department of Chemistry, University of Texas at Dallas, Richardson 75083-0688.
Lazar
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Brucher
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Sherry
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AD
Malloy
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CR
D002413:Cations, Divalent / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D008274:Magnesium / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009943:Organophosphorus Compounds; D010761:Phosphorus Radioisotopes
D002413:Cations, Divalent; D009943:Organophosphorus Compounds; D010761:Phosphorus Radioisotopes; C068116:1,4,7-triazacyclononane-N,N',N''-tris(methylenephosphonate monoethyl ester); D008274:Magnesium