Abstract
Abstract By using a conventional FT NMR spectrometer and probe, we first detected 43 Ca NMR spectra of the Ca 2+ (2.9 mM): calmodulin (0.725 mM) (1:1 per binding site) complex in 0.15 M N -2-hydroxyethylpiperazine N′ -2-ethanesulfonic acid (HEPES)–K + buffer (pH 7.2). The half-band width of the complex was nearly 160 Hz and the signal of the complex was located at the 2.13 ppm (43 Hz) lower field from that of the free Ca 2+ ion. By adding trifluoperazine, melittin, substance P or glucagon, the half-band widths of the Ca 2+ –calmodulin complex (1:1 per binding site) were remarkably reduced and the chemical shifts of the complex moved back to the upper field. It is suggested that the Ca 2+ ion may bind to Ca 2+ low-affinity sites more tightly in the presence of those effectors than in their absence.
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