PHOSPHORYLATION OF THE ALPHA-POLYPEPTIDES AND BETA-POLYPEPTIDES OF THE LIGHT-HARVESTING COMPLEX-I (B870) OF RHODOBACTER-CAPSULATUS IN AN IN-VITRO TRANSLATION SYSTEM

Synthesis and phosphorylation of the proteins alpha and beta of the light-harvesting (LH) complex I (B870) were investigated in a cell-free translation system of Rhodobacter capsulatus. Both proteins were incorporated into the membrane fraction; LHI beta was inserted in the absence of LHI alpha. LHI alpha was phosphorylated in the presence of [gamma-P-32]ATP only when membranes were present. Phosphorylated LHI beta was found only in the absence of membranes. The phosphate group bound to LHI beta was not transferred to LHI alpha during insertion. The results indicate that a membrane-bound and a soluble protein kinase are involved. Strong light reduced the amount of phosphorylated LHI alpha. The results are discussed with respect to the assembly and function of LHI.