The longitudinal relaxation rates of the adenosine AH(8), AH(2), AH(1′), and the pantetheine PH(3′) protons of coenzyme A (CoA) were measured in solutions of free CoA (0.062 M) and for the CoA-Mn(II) complex. The experiments were carried out in D2O at slightly basic values of the pH at 100.0 MHz and at 298 K. By observing the paramagnetic effects of the weakly bound metal ion on the proton longitudinal rates, distances were calculated between the Mn(II) ion and these four protons. For the complex containing two water molecules, the four distances are 4.8 ± 0.5 Å (1 Å = 0.1 nm) to the AH(8) proton, 6.5 ± 0.6 Å to the AH(2) proton, 6.4 ± 0.6 Å to the AH(1′) proton, and 6.0 ± 0.6 Å to the pantetheine PH(3′) proton. For three water molecules, the four distances are 4.5 ± 0.5, 6.1 ± 0.6, 5.9 ± 0.6, and 5.6 ± 0.6 Å, respectively. The correlation times have been determined previously, based on water proton longitudinal relaxation measurements, and these are 6.6 × 10−10 s for the first case and 4.0 × 10−10 s for the latter case. Experiments were also carried out on 0.010 M CoA solutions and, within experimental error, the distances remained unchanged.These distances, combined with the Mn(II) ion to the phosphorus nuclei distances, together with a knowledge of the conformation of the free CoA in solution are used to construct models for the conformation of the CoA–Mn(II) complex in solution. These results are compared with the available data for the Mn(II)–ATP complex, with the lanthanide ion complexes with dephospho CoA, and with the Co(II) ion complexes with propionyl CoA and the enzyme transcarboxylase.
The use of gadolinium as a probe in the Fc region of a homogeneous anti-(type-III pneumococcal polysaccharide) antibody