Correlation of membrane protein phosphorylation with excitation energy distribution in the cyanobacteriumSynechococcus6301

Synechococcus cells grown on [ 32 P]orthophosphate exhibit light‐dependent phosphorylation of polypeptides at 18.5 kDa (soluble fraction) and 15 kDa (membrane fraction). The 15 kDa polypeptide is also phosphorylated in the light in isolated Synechococcus thylakoids incubated with [γ‐ 32 P]ATF. 77 K fluorescence emission spectra of both cells and thylakoids show increased photosystem I emission and decreased photosystem II emission under conditions required for protein phosphorylation. We propose that membrane protein phosphorylation regulates distribution of absorbed excitation energy between the two photosystems in Synechococcus and other phycobilisome‐containing organisms, and that lateral heterogeneity in thylakoid organization is not a necessary condition for protein phosphorylation‐dependent adaptations to changing wavelength of light.