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The acyl carrier protein (ACP) of Escherichia coli is a 77‐amino acid, highly negatively charged three‐helix protein that plays a central role in fatty acid biosynthesis. Previous NMR studies have suggested the presence of multiple conformations and marginally stable secondary structural elements. The stability of these elements is now examined by monitoring amide exchange in apo‐ACP using NMR‐based methods. Because ACP exhibits many rapid exchange rates, application of traditional isotope exchange methods is difficult. In one approach, heteronuclear correlation experiments with pulsed field‐gradient coherence selection have reduced the time needed to collect two‐dimensional ¹H‐¹⁵N correlation spectra to the point where measurement of exchange of amide protons for deuterium on the timescale of minutes can be made. In another approach, water proton selective inversion‐exchange experiments …