Increased tolerance to thermal inactivation of oxygen evolution in spinach Photosystem II membranes by sustitution of the extrinsic 33-KDa protein by its homologue from a thermophilic cyanobacterium

Abstract

Photosynthetic oxygen evolution is an extremely heat-sensitive process and incubation of spinach Photosystem II (PSII) membranes at 40ºC for only several minutes leads to its complete inactivation. Substitution experiments of the spinach 33-kDa manganese stabili<ing protein by a homologue protein, isolated either from the thermophilic cyanobacterium Phormidium laminosum, or from Escherichia coli as a recombinant thermophilic cyanobacterial protein, showed a significant increase in tolerance to heat inactivation of the oxigen-evolving activity. The results allow us to suggest that thermalinactivation of oxygen evolution in higher plant PSII membranes is due to dissociation of the 33-kDa protein as a consequence of temperature-induced conformational changes, and stabilization can be provided by sustitution by a thermostable homologue whose secondary structure and binding to PSII remain ulatered at moderately hight temperature.