Abstract
The green alga Chlamydomonas reinhardtii contains nine distinctive LHCIs; seven out of nine accumulate at a stoichiometoric amount with PSI subunits and the remaining two are present at a lower level. Since LHCIs associate stably with PSI complex, they are purified as PSI-LHCI supercomplex in the presence of a nonionic detergent. In order to characterize the structure/function relationship of PSI-LHCI supercomplex, we have developed an efficient method for the supercomplex purification. Thylakoid membranes were solubilized with dodecyl-maltoside, fractionated on sucrose density gradient, and subsequently purified by anion exchange column chromatography. We optimized sucrose density gradient for ultracentrifugation and NaCl gradient in elution buffer of DEAE chromatography for the satisfactory purification of a larger amount of PSI-LHCI supercomplex. The resulted preparation retains most constituent polypeptides except two peripheral subunits and shows a high PSI activity. The present purification method can be applied for PSI-LHCI supercomplex on a large scale.
