Conformation of adenosine-5′-triphosphate in the presence of Mg2+ at different pH

NOESY experiments have been performed on adenosine-5'-triphosphate (ATP) in the presence of 1:1 Mg2+ (MgCl2) at different pH. The results show that H8-H1' and H8-H2' interproton NOE intensities change with pH, with nearly equal intensity at low pH (pH 1.9) and with H8-H2' signal stronger than the H8-H1' signal at higher pH (between 3.7 and 8.5). The H8-H1' and H8-H2' distances and the C4-N9-Cl'-O4' torsion angle (chi) have been measured from random structures of adenosine and ATP. It is concluded that the lower pH allows the formation of a P-gamma-O-Mg2+-N1 bridge and the torsion angle takes a cis conformation accordingly. (C) 2002 Elsevier Science Ltd. All rights reserved.