At pH 6.5, the RCs became unstable and no spectra could be obtained. ND(M199) mutant The Special TRIPLE spectra of ND(M199) RCs at pH 6.5, 8.0, and 9.5 are shown in Fig. 5. At pH 8.0, the two large β-proton hfcs are shifted to higher values compared to wild type and a third strongly coupled β-proton is visible. Four intense and narrow lines are present that are assigned to methyl groups. Assuming both larger methyl hfcs belong to the L-side and the two smaller hfcs to the M-side, ratios

of 1.79 and 1.57 are calculated, respectively, which are both very different from the values of BMN 673 mouse 2.4 and 1.4 found for wild type and most mutants (Rautter et al. 1995). However, an assignment of the hfcs with 6.32 and 2.59 MHz to one

side yields a ratio of 2.44 that would fit very nicely to the M-side but the remaining two lines yield a ratio of 2.18 that does not fit to the L-side at all. The assumption that the signal at 2.59 MHz represents an overlap of L-side and M-side methyl hfcs signals solves this problem, as the ratio of 3.54/2.59 is equal to 1.37, which is the expected ratio for the L-side (Table 1). selleck screening library This assumption leaves the smallest signal of 1.62 MHz unassigned. Fig. 5 1H-Special TRIPLE spectra (X-band) of light-induced P•+ from RCs from Rb. sphaeroides mutant ND(M199) at pH 6.5 (green), 8.0 (red), and 9.5 (black). The isotropic hyperfine couplings aiso are directly obtained from the Special TRIPLE frequency by ν ST = a iso/2 (for details see Lendzian et al. 1993). Assignments of the lines to molecular positions of the

L- and the M-half of the BChl-dimer are given (cf. structure in Fig. 1c) The pH dependence for the P/P•+ midpoint potential of this mutant between pH 6.5 and 9.5 was well described using the Henderson–Hasselbalch equation with a pK a of 7.9 (Williams et al. 2001). Consequently, we can expect at pH 8.0 a contribution of two different species, one protonated and the other deprotonated (if the rate constants are slower than the time resolution of the TRIPLE experiment, see discussion above). Comparison with the spectra at pH 9.5 and 6.5 shows that some lines change intensity. This pH difference seems to indicate the presence AMP deaminase of two species that could be associated with the protonated and the deprotonated state of the Asp residue. The high pH form (deprotonated) has more spin density on PM and the low pH form (protonated) is similar to wild type with a dominant PL spin density. A species with several lines similar to those of wild type can indeed be found in the spectrum of this mutant at pH 6.5 (already present with lower intensity at pH 8.0) (see Fig. 5). HE(L168) and HE(L168)/ND(L170) mutants Special TRIPLE spectra of HE(L168) RCs were recorded at pH 8.0 and 6.5 (data not shown).