Changes in cooperativity of the light-harvesting system of Rhodospirillum rubrum were monitored in whole cells by measurements of in vivo bacteriochlorophyll fluorescence yield transients. Under non-cooperative conditions a polypeptide of 10.5 kDa (provisionally identified as B880-β) was specifically phosphorylated; under cooperative conditions a polypeptide of 13 kDa (provisionally identified as B880-α) was specifically phosphorylated. These results are discussed in relation to the regulation of excitation energy distribution in purple photosynthetic bacteria and other photosynthetic organisms.
