ИСТИНА

Kinetics of forward and backward electron transfer (ET) reactions were measured in photosystem I (PS I) complexes of cyanobacterium Synechocystis sp. PCC 6803 in solution and in dry trehalose glassy matrix at room temperature. Immobilization in disaccharide matrix resulted both in complete arrest of forward ET reactions in a fraction of PS I and in slowdown of forward ET from the quinones A1 to the terminal iron-sulphur clusters by a factor of 10-50 in the remaining complexes. The kinetics of charge recombination from various cofactors were almost unaffected. The data obtained were compared with recombination kinetics in PS I measured over a temperature range from 4 to 290 K. The kinetics (A) and amplitudes (B) of charge recombination demonstrate similar progressive arrest of forward ET upon temperature decrease. However, it is accompanied by temperature-dependent slowdown of recombination reactions from terminal electron acceptors and by rising heterogeneity of ET reactions. The similarities and distinctions between the effects of restricted protein mobility due to freezing of the protein in water-glycerol mixture and due to immobilization in rigid trehalose matrix are discussed.