Isolation Of 32-35 Kda Thylakoid Proteins From Chlamydomonas-Reinhardii

The protein composition of Chlamydomonas reinhardii thylakoids in the molecular weight range of 32-35 kDa was studied. The thylakoids were labelled with 32P-Pi in vivo using Pi-starved cell cultures, solubilized with SDS and separated by polyacrylamide gradient gel electrophoresis. The following differentiation of proteins could be accomplished: two proteins were phosphorylated, which were also well stained with Coomassie blue, and one major protein was only detected by the silver staining procedure. The mobility of the latter protein is different in gels with urea, showing an apparently lower molecular weight. In order to investigate whether a functional photosystem II is obligatory for protein phosphorylation, the phosphorylation of thylakoid proteins was studied with a photosystem II deficient mutant. The mutant, which had normal photosystem I activity, but lacked photo- system II activity, could synthesize ATP light dependently; its main labelled protein bands had a molecular weight of 32-35 kDa; it contained the light harvesting protein chlorophyll complex and an unknown protein at 22 kDa. The 32P incorporation in photosystem II deficient cells was comparable to cells with functional photosystem II units.