Enzymes manganese

In a study on another manganese enzyme, glutathione transferase, the Hoffmann group has proposed Q-band dispersion EPR at the unusually low temperature of 2 K as the optimal approach to collect data from Mn11 centers with D hv (Smoukov et al. 2002). This proposal would be practically limited by the fact that Q-band spectrometers running at 2 K can be counted on the fingers of one finger however, dispersion spectra are readily obtained in Q-band also at helium-flow temperatures (i.e., T>4.2K). 

M.S. Lah, M.M. Dixon, K.A. Pattridge, W.C. Stallings, J.A. Fee, and M.L. Ludwig, Structure-function in Escherichia coli iron superoxide dismutase comparisons with the manganese enzyme from Thermus thermophilus. Biochemistry. 34, 1646-1660 (1995). 

Catalases catalyze the conversion of hydrogen peroxide to dioxygen and water. Two families of catalases are known, one having a heme cofactor and the second a structurally distinct family, found in thermophilic and lactic acid bacteria. The manganese enzymes contain a binuclear active site and the functional form of the enzyme cycles between the (Mn )2 and the (Mn )2 oxidation states. When isolated, the enzyme is in a mixture of oxidation states including the Mn /Mn superoxidized state and this form of the enzyme has been extensively studied using XAS, UV-visible, EPR, and ESEEM spectroscopies. Multifrequency EPR and microwave polarization studies of the (Mn )2 catalytically active enzyme from L. plantarum have also been reported. ... 

A manganese-containing YADH has been obtained from yeast grown in a zinc-free, manganese-rich medium.12 4 The enzyme was found to have four atoms of metal per enzyme molecule, all of which were manganese. This manganese enzyme is much less stable than the native zinc enzyme and the kinetic parameters are different. 

In the recent years, our work on the PS-II reaction center has mainly involved EPR spectroscopy, to identify and understand the functional properties of the secondary acceptors, essentially two quinones QA and QB interacting with a Fe2+ iron, and of the manganese enzyme which realizes the oxidative cleavage of water (see e.g. Beijer and Rutherford, 1987 or Styring and Rutherford, 1987). The recent development of a method permitting to simply isolate a PS-II reaction center core (Nanba and Satoh, 1987) allowed us to study the primary radical-pair (P-680+, I ). We first worked in collaboration with the Japanese group, then developed our own preparation (Hansson et al., 1987 Frank et al., 1987 Takahashi et al., 1987) and also collaborated with the group of Professor Barber (London, UK). 

Kinetic studies of the Fe(SOD) indicate a fairly simple oxidation-reduction cycle in which 02 is bound to the Fe(III) form of the protein and oxidized to 02, followed by binding of a second 02 to the resulting Fe(II) form and reduction to H202. The kinetics of Mn(SOD) are more complicated and the turnover number (1300 s-1 at 25 °C) is much lower than for Fe(SOD) (26,000 s-1) however, a similar catalytic cycle is believed to occur. The manganese enzyme kinetics are complicated by a side reaction to form a dead end complex, possibly a Mn(III) peroxide complex (61, 62). 

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