A magnetic resonance study of the coenzyme A--manganese(II) complex in solution.
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Buffers↗
Biomedical subjects
G Kotowycz
Publications and source records attributed to G Kotowycz.
The nature of the coenzyme A--manganese(II) complex in solution as studied by proton magnetic resonance.
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Chemical Phenomena↗
The stoichiometry and stability of the NADP complexes with manganese(II) ions as studied by electron paramagnetic resonance.
Magnetic resonance techniques have been applied to study the stability of the complexes formed between Mn(II) ions and NADP in aqueous solutions at a pH of 7.5 and 20 degrees C. The electron paramagnetic resonance (epr) data indicate that at low Mn(II) ion concentrations ([Mn(II)] less than 1 mM; [NADP] approximately 5 mM), a 1:1 complex is formed with an apparent stability constant K1 = 370 +/- 50 M-1 at an ionic strength of 0.22 in the presence of 0.20 M Cl-. At high Mn(II) ion concentrations, a Mn(II)2-NADP species, with an apparent stability constant K2 = 54 +/- 17 M-1, is present in significant amounts. When the epr data are corrected for the presence of the MnCl+ ion, the analysis of the new Scatchard plot yields stability constants for the two sites of K1 = 640 +/- 90 M-1 and K2 = 88 +/- 13 M-1, respectively. The presence of two metal ion binding sites on the NADP molecule has not been observed previously, and previous workers have always analyzed their data in terms of the 1:1 Mn(II)-NADP complex. An epr temperature study of K1 yields a value of delta H equal to 1.3 +/- 0.2 kcal/mol (1 cal = 4.187 J).
Chemical Phenomena↗
Nuclear magnetic resonance relaxation time studies on the manganese(II) ion complex with succinyl coenzyme A synthetase from Escherichia coli.
Nuclear magnetic resonance, as well as electron paramagnetic resonance, experiments were carried out in a study of the Mn(II) ion complex with phosphorylated succinyl-CoA synthetase. For high specific activity enzyme samples, there are 3.5 +/- 0.7 metal ion binding sites per enzyme molecule with indistinguishable dissociation constants (KD = 6.9 X 10(-4) M). However, for enzyme samples with a lower specific activity yet equivalent purity, there are 1.6 strong metal ion binding sites (KD = 6.6 X 10(-4) M) and 2.0 weak metal ion binding sites (KD = 4.0 X 10(-3) M), a result that is easily reconciled with the alpha2beta2 subunit structure of the enzyme. Water proton relaxation rate measurements indicate that each strongly bound Mn(II) ion is coordinated to three water molecules. The present results strongly suggest that the existence of nearly 4 high-affinity metal binding sites per enzyme molecule is related to the integrity or configuration of that portion of the molecule which interacts with substrates.
Binding Sites↗