[Effect of secondary structure on the rate dark reduction of P700+ with ascorbate of the photosystem I complex]

Relationship was studied between the spectra of KD, absorption and fluorescence and kinetics of P700+ dark reduction with exogenous donor and sodium dodecyl concentration inducing a conformation transition of the protein globule. It has been shown that with a decrease of the detergent concentration from 0.01 to 0.06% an increase of the portion of the protein globule-helical regions (from 10 to 30%) and an essential decrease of the time of P700+ dark reduction with ascorbate take place. The changes of KD, absorption and fluorescence spectra of chlorophyll a observed in the same region of detergent concentration do not correlate with the changes of the secondary structure of the protein part of the pigment-protein complex. It is suggested that accelerated reduction of P700+ with ascorbate is conditioned by an increase of accessibility of exogenous donor to the reaction centre resulting from conformation changes of the complex protein part.