Heat inactivation of electron transport reactions in photosystem II particles

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Abstract
Heat inactivation of diphenylcarbazide (DPC)‐supported 2,6‐dichloroindophenol (DCIP) photoreduction by photosystem II (PS II) particles and non‐oxygen‐evolving PS II core complex isolated from spinach (Spinacia oleracea L. cv. Kyoho) was suppressed under annealing conditions, and accelerated in the presence of EDTA or high concentration of divalent cations. After heating at 45°C for 10 min, half‐maximal annealing effects occurred at 35°C. Minimum acceleration was observed in the presence of 1 mM Mg2+, implying the existence of a cation‐specific site in the vicinity of the PS II reaction center. The acceleration depended on the temperature at which EDTA was added to PS II particles. Half‐acceleration by EDTA occurred at 35°C. Glutaraldehyde stabilized PS II particles against heat inactivation of PS II photochemical reactions.