Abstract
Both ATP and a bivalent nucleotide-bound metal activator, normally Mg 2+, are required for nitrogenase activity. EPR and ESEEM (electron spin-echo envelope modulation) measurements have been carried out on adenosine nucleotides in which the Mg2+ ion that is usually bound is replaced by Mn2+ in the presence of Kp2 (nitrogenase Fe-protein from Klebsiella pneumoniae). The Mn2+ zero-field splitting parameters have been determined from the EPR-spectrum to be |D| = 0.0125 cm-1 with a rhombicity λ = E|D = 0.31 by direct diagonalization of the complete spin Hamiltonian. ESEEM spectra of the Fe-protein with MnADP and MnATP both show an ESEEM line pair with one signal component at about 3.6MHz and a relatively broad resonance at 8 MHz originating from a superhyperfine coupling to a 31P nuclear spin from one or more directly co-ordinated phospho group(s) of the nucleotide. A pronounced resonance overlapping the low-frequency component of the 31P-signal at about 3.5 MHz is attributed to an interaction of Mn2+ with univalent 23Na nuclei. ESEEM lines at frequencies
Original language | English |
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Pages (from-to) | 527-539 |
Number of pages | 12 |
Journal | Biochemical Journal |
Volume | 391 |
Issue number | 3 |
DOIs | |
Publication status | Published - 1 Nov 2005 |
Keywords
- Electron paramagnetic resonance (EPR)
- Electron spin-echo envelope modulation (ESEEM)
- Fe-protein
- Hydrolysis
- Manganese
- Nitrogenase