Polypeptide Composition of Chlorophyll-Protein Complexes from Romaine Lettuce

Abstract

The protein moiety of the two major chlorophyll-protein complexes associated with chloroplast membranes of outer, dark green leaves of a romaine lettuce shoot (Lactuca sativa L. var. Romana) has been analyzed by discontinuous sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Complex II, also termed light-harvesting chlorophyll-protein complex, is shown to consist of a major polypeptide of 25 kilodaltons (kD) and two minor ones of 27.5 and 23 kD. The 25 kD subunit is the single largest polypeptide component of the chloroplast membranes, accounting for about 25% of their total protein. Complex I contains only high molecular weight subunits, the major one being at 67 kD, these subunits representing only a small percentage of the chloroplast membrane total protein.These data, suggesting an oligomeric nature for the apoprotein of these two chlorophyll-protein complexes, are difficult to reconcile with the estimated molecular weights of the native complexes and raise some intriguing questions as to the types of interactions among the components of these major lipoproteins of the photosynthetic membranes.