Abstract
Light-harvesting chlorophyll a/b complex I (LHCI) is stably associated with photosystem I (PSI) core complex. In higher plants, six distinctive LHCI polypeptides are found and four out of six were identified in crystal structure of PSI-LHCI supercomplex. In the green algae, Chlamydomonas reinhardtii, nine distinctive LHCI subunits were identified in PSI-LHCI supercomplex. However, the copy numbers of LHCI in PSI-LHCI supercomplex remains elusive. Here we report quantitative estimation of LHCI polypeptides in PSI-LHCI supercomplex by radio-labeling with 14C. The PSI-LHCI-supercomplex was purified from C. reinhardtii cells after total cell proteins had uniformly labeled with [14C] acetate. The stoichiometry of the polypeptides in PSI-LHCI supercomplex was determined by measuring the radioactivity detected by radioluminography. We optimized electrophoresis conditions for SDS-PAGE to separate nine LHCI polypeptides as distinctive bands. We will also discuss structure of LHCIs in PSI-LHCI supercomplex.
