A nuclear magnetic resonance study of pyridoxal phosphate – metal ion interactions. II. Binding of manganese(II)

Abstract

The line width and spin–lattice relaxation rates of phosphorus and proton nuclei in PLP have been measured as a function of temperature in the presence of Mn(II) using pulsed nmr methods. The T_1M of ³¹P in PLP-Mn(II) is very close to the T_1M values of β- and γ-phosphorus atoms in ATP–Mn(II) at ∼40 °C. The T₁ data of ³¹P and ¹H have been interpreted in terms of the dipolar interaction between the electron and nuclear spins. With the assumption that the Mn(II) interacts directly with the phosphate of PLP the rotational correlation time τ_c at 38 °C was calculated to be 7.6 × 10⁻¹⁰ s from phosphorus T₁ data. This τ_c value was subsequently used to calculate metal–proton distances from proton T₁ and T₂ data. The results lead to the conclusion that the phosphate-bound metal interacts directly with the aldehyde oxygen in a 1:1 PLP–Mn(II) complex. The linewidth of the ¹³C resonances of PLP in the presence of Mn(II) supports this conclusion. The structure assigned for PLP–Mn(II) complex is in conformity with the structure for PLP-Co(II) complex.