ASSIGNMENT OF FUNCTION TO POLYPEPTIDES OF 32–34 KILODALTONS IN THYLAKOIDS

Publisher Summary This chapter describes the assignment of function to polypeptides of 32–34 kDa in thylakoids. Various functions have been ascribed to the polypeptides in the 32–34 kDa size class including protective or shield role for the phototsystem II (PS II) reaction center, formation of the herbicide binding site, the apoprotein of B, participation in the process of water oxidation, and the site of Mn ++ binding. Two polypeptides of similar molecular weight can be resolved on LDS-PAGE systems containing 4M urea. The protein running at 33 kDa in this system can be easily extracted from membranes or PS II particles and purified. It is a lysine-rich polypeptide that, upon removal, makes Q – accessible to ferricyanide in an herbicide-insensitive reaction. It, therefore, fulfills the requirements of the PS II shield-protein. A polypeptide that runs at 31 kDa in 4M urea/SDS PAGE binds azido–atrazine and is designated as the herbicide binding polypeptide.