Nuclear magnetic resonance study of the complexes of manganese(II) and fully adenylylated glutamine synthetase (Escherichia coli W). Frequency, temperature, and substrate dependence of water proton relaxation rates

Manganese(II) as magnetic relaxation probe in the study of biomechanisms and of biomacromolecules

“…It was instead postulated that fast exchange conditions apply, that T1M 1 is a maximum, and that rs, which is itself frequency dependent, is the effective correlation time especially at low temperatures and low frequencies. 115,118,[119][120][121][122][123][124][125][126][127][128][129] The inclusion of rM in the determination of Tjn-1 was also excluded on the basis of the small energy of activation obtained from the Arrhenius plot of Tlp-1 vs. l/T130,131. rM was shown to become important at high temperature whenever outer-sphere relaxation is the only relaxation mechanism108,132 since, in that case, the rM > T1M condition is easily reached.…”

Calorimetric and equilibrium binding studies of the interaction of substrates with glutamine synthetase of Escherichia coli

“…preparation appeared to contain a high percentage of unadenylylated dodecamers and, conversely, a low percentage of hybrids in preliminary experiments of J. Davis and E. R. Stadtman e This paper, Figure 5A Y Denton and Ginsburg (1969). * Villafranca and Wedler (1974). The state of adenylylation of the etrxi'-e preparation used by Villafranca and Wedler is uncertain because the adenylylation state of glutamine synthetase isolated from E. coli W ceiK crown under the conditions of Woolfolk et al (1966) varies.…”

“…With Mn2+ bound at both n\ and n2 subunit sites of GS-, L-glutamine (50 mM) or ADP (0.25 mM) decreased from 4 to ~2 the number of rapidly exchanging water molecules in the primary coordination shells of bound Mn2+. As stated by Villafranca and Wedler (1974), a decrease in the number of rapidly exchanging water molecules from the primary coordination sphere of bound Mn2+ can arise either from displacement of a water ligand by a substrate or protein ligand or by restriction of a water ligand on the bound Mn2+ so that its exchange is slow compared with the other water molecules. Since Mn2+ can bind to n2 subunit sites as the ADP-Mn complex (Hunt et al, 1975), the PRR results with ADP present are consistent with substrate substitution into the coordination sphere of Mn2+ bound at n2 sites.…”

Differences in iron and manganese concentration may confound the measurement of myelin fromR1andR2relaxation rates in studies of dysmyelination

“…whether the changing metal is predominantly in the form of free ions or bound to proteins . The relaxivity of enzyme‐bound Mn 2 + is different from that of free aqueous Mn 2 + . In addition, aggregated liposomal ferritin has higher per‐ion r 2 relaxivity than free ferritin , which has higher relaxivity than free Fe(II) .…”