A soluble cytochrome (Cyt) c' from thermophilic purple sulfur photosynthetic bacterium Thermochromatium (Tch.) tepidum exhibits marked thermal tolerance compared with that from the closely related mesophilic counterpart Allochromatium vinosum. Here, we focused on the difference in the C-terminal region of the two Cyts c' and examined the effects of D131 and R129 mutations on the thermal stability and local heme environment of Cyt c' by differential scanning calorimetry (DSC) and resonance Raman (RR) spectroscopy. In the oxidized forms, D131K and D131G mutants exhibited denaturing temperatures significantly lower than that of the recombinant control Cyt c'. In contrast, R129K and R129A mutants denatured at nearly identical temperatures with the control Cyt c', indicating that the C-terminal D131 is an important residue maintaining the enhanced thermal stability of Tch. tepidum Cyt c'. The control Cyt c' and all of the mutants increased their thermal stability upon the reduction. Interestingly, D131K exhibited narrow DSC curves and unusual thermodynamic parameters in both redox states. The RR spectra of the control Cyt c' exhibited characteristic bands at 1,635 and 1,625 cm(-1), ascribed to intermediate spin (IS) and high spin (HS) states, respectively. The IS/HS distribution was differently affected by the D131 and R129 mutations and pH changes. Furthermore, R129 mutants suggested the lowering of their redox potentials. These results strongly indicate that the D131 and R129 residues play significant roles in maintaining the thermal stability and modulating the local heme environment of Tch. tepidum Cyt c'.

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Rhytidiumlight-induced controlled by activated by desiccation. One of them permits exciton migration tewards a farred band in the antenna pigments whcre fast thermal deactivation takes plaee. This mechanism appears te be similar to a mechanism detected before in desiccated ]ichens, A third mechanism is based on the reversible photoaccumulation of a radical that acts as a quencheT of excitation energy in reaetion centres ef photosystem Il. On the basis of absorption changcs around 800 nm, the quencher is suggested to be an oxidized chlorophyl]. The data show that desiccated moss is better protected against photo-oxidative damage than hydrated moss, Slow drying of moss thalli in the light increases photoprotectien rnore than s]ow drying in darkness, ]trNma1[6itUtnfn#"63DopiHveIM"l Three different mechanisms of energy dissipation ofa desiccation-toterant mess to protect reaction centres against photo-oxidation , Yoshimasa Fukushiinat, Shigeru Itohi, Ulrich Heber? Sci., Uhiv. Ndgaya, ?Bio. Sc'i., Univ. PFItmburg) types of non-photoehernical de-excitation of absorbed light photosystem II of the sun-and desiccation-tolerant moss rugosum against photo-oxidation. The first mechanism, which is in hydrated thalli, is sensitive to inhibition by dithiothreitol. It is