Two-dimensional 1H-NMR investigation of the water conformation of the atrial natriuretic factor (ANF 101-126)

The complete sequential assignment of the ¹H-nmr resonance frequencies of the active fragment of the rat atrial natriuretic factor (ANF 101–126) has been performed. Two-dimensional nmr techniques have been employed, including phase-sensitive nuclear Overhauser spectroscopy (NOESY), relayed coherence transfer spectroscopy (RELAY), and J-correlated spectroscopy (COSY). Experiments were performed both in D₂0 and H₂0 solutions at different pH values. With few exceptions, resonance frequencies were practically pH independent. NOESY spectra were recorded using both 300- and 500-ms mixing times, and no long-range connectivities were observed, leading to the conclusion that ANF 101–126 has no defined secondary nor tertiary structure in water in the pH range used (2.73–5.21).