Reversal of dibromothymoquinone inhibition of photosynthetic electron transport by bovine serum albumin

Abstract

Addition of bovine serum albumin to cholorplasts inhibited by prior addition of 1 [mu] dibromothymoquinone results in a time- and light-dependent restoration of electron transport activity. The kinetics of this reversal reaction are complex, and indicate that it is controlled by the degree to which the thylakoid membranes are energized. The presence of ADP and inorganic phosphate, or of uncouplers, serves to retard the rate of reversal, whereas an acceleration of reversal is observed if the thylakoid membranes have been intentionally unstacked by exposure to low-salt medium. The reversal reaction reported here is unique to bovine serum albumin, and does not require the function of the free sulfhydryl group on the protein. It is concluded that the site of DBMIB inhibition associated with chloroplast membranes is situated in a position whose access to contact by bovine serum albumin is regulated by the structural changes induced by illumination and energization.