The P700 chlorophyll a-protein was purified by preparative sodiumdodecyl sulfate (SDS) gel electrophoresis from SDS- olubilized barley (Hordewm vulgare L., cv Himalaya) chloroplast membranes. After elution from the gel in the presence of 0.05 to 0.1% Triton X-100, the recovered protein had a chlorophyll/P70. Ratio of 50 to 60/1 and contained no chlorophyll b or cytochromes. Analysis of the polypeptide composition of the chlorophyll-protein revealed  58 to 62 kilodalton (kD) polypeptide component but no lower molecular weight polypeptides. The 58 to 62kD component was further  resolved into  two distinct polypeptide bands  which were subsequently mapped by partial cyanogen bromide digestion and Staphylococcus aureus proteolysis. Based on results from the mapping experiments and other data, we suggest that the two components are conformational variants of a single polypeptide. Measurement of the chlorophyll to protein ratio by quantitative amino acid analysis and consideration of the yield of P700 in the protein isolate suggest that, contrary to previous models (Bengis and Nelson, 1975, 1977), P700 in vivo is associated with a minimum of four subunits of approximately 60 kD.

Antibodies raised against the photochemically active chlorophyll-protein complex from barley reacted specifically with the 58 to 62 kD apoprotein. The same preparative electrophoresis procedure was used to isolate photo chemically active P700 chlorophyll a- rotein from soybean (Glycine max L.), tobacco (Nicotiana tabacum L.), petunia (Petunia x hybrida), tomato (Lycopersicum esculentwm), and Chiamydomonas reinhardti. The isolated complex from all species exhibited identical polypeptide compositions and chlorophyll/P7.. ratios. Antibodies to the barley protein cross reacted with all species tested demonstrating the highly conserved structure of the apoprotein.