Is the primary cause of thermal inactivation of oxygen evolution in spinach PS II membranes release of the extrinsic 33 kDa protein or of Mn?

A Domain of the Manganese-stabilizing Protein fromSynechococcus elongatus Involved in Functional Binding to Photosystem II

“…Residues-There are several lines of evidence indicating that binding of MSP to its functional site involves electrostatic interactions between charged amino acid residues on the protein and oppositely charged residues on intrinsic proteins of PSII (6,7,36,37). Single-amino acid substitution experiments were, therefore, performed for conserved, charged residues located in the two protease-sensitive sequences.…”

IV.Heat stress in Triticum: kinetics of Fe and Mn accumulation

“…Yet, when temperatures rise c.a. 45ºC (Çjánek et al, 1998(Çjánek et al, , Yamane et al, 1998, the thermal damage of the photosynthetic oxygen evolving complex (Enami et al 1994, Mohanty et al 2002 affects the electron transport (Bukhov et al, 1999;Kouřil et al, 2004;Mohanty et al, 2002). In the heat stressed Triticum, the alteration of chloroplasts structure (namely, grana stacking) has further been reported (Sharkova and Bubolo, 1996), with moderate high temperatures triggering a thylakoid permeability deviation that affects the proton gradient (Bukhov et al, 1999;Schrader 2004), the cyclic photophosphorylation and eventually the b 6 /f cytochrome complex (Sharkey 2005).…”

Function of Extrinsic Proteins in Stabilization of the Photosynthetic Oxygen-Evolving Complex

“…The PsbO protein can be dissociated from the PSII by a variety of chemical treatments including washing with alkaline Tris buffer, a high concentration of CaCl 2 , and chaotropic agents [Enami et al, 1994, Ghanotakis & Yocum, 1990. In particular, Lys residue-modifying chemicals such as Nsuccinimidyl propionate and 2,4,6-trinitrobenzene sulfonic acid caused release of PsbO from PSII and loss of oxygen-evolving activity [Miura et al, 1997], suggesting that the positive charge of Lys is important for the electrostatic interaction between PsbO and PSII.…”

“…Previous in-vivo and in-vitro studies have estimated the heat-labile properties of the OEC [Berry & Bjorkman, 1980, Havaux & Tardy, 1996, Mamedov et al, 1993. These studies demonstrated that the release of PsbO occurs first, followed by liberation of two of the four Mn ions from the Mn 4 Ca cluster of the OEC [Enami et al, 1998, Enami et al, 1994, Nash et al, 1985, and finally by the loss of oxygen evolution at high temperatures [Enami et al, 1994, Yamane et al, 1998]. …”