Properties of a peripheral 34 kDa protein in Synechococcus vulcanus Photosystem II particles. Its exchangeability with spinach 33 kDa protein in reconstitution of O 2 evolution

Abstract

Photosystem II (PS II) particles retaining a high rate of O 2 evolution were prepared from a thermophilic cyanobacterium, Synechococcus vulcanus Copeland, and the composition and properties of their peripheral proteins were investigated. The following results were obtained. (1) The O 2-evolving PS II particles of S. vulcanus contained only one peripheral protein with a molecular mass of 34000 which corresponded to the 33 kDa protein in higher plant PS II particles, but no other peripheral proteins corresponding to the 24 and 16 kDa proteins of higher plant PS II particles. (2) The cyanobacterial peripheral 34 kDa protein was removed from the particles by 1 M CaCl 2-washing concomitant with total inactivation of O 2 evolution, and the inactivated O 2 evolution was reconstituted to 75% of the original activity by rebinding of this protein back to the washed particles. (3) The cyanobacterial peripheral 34 kDa protein rebound to CaCl 2-washed spinach PS II particles and restored O 2 evolution to an appreciable extent (28%). (4) The spinach peripheral 33 kDa protein rebound to CaCl 2-washed PS II particles of S. vulcanus and partially restored O 2 evolution (60%). These results suggested that the peripheral 34 kDa protein of S. vulcanus possesses the determinants for both binding and activity reconstitution identical with those of the peripheral 33 kDa protein of spinach.