COMPARISON OF A CHLOROPHYLL A-PROTEIN COMPLEX ISOLATED FROM A BLUE-GREEN ALGA WITH CHLOROPHYLL-PROTEIN COMPLEXES OBTAINED FROM GREEN BACTERIA AND HIGHER PLANTS

1. 1. An improved procedure has been devised for the purification of large quantities of a detergent-soluble chlorophyll a-protein complex (λmax 677 nm) from a blue-green alga. The complex, which is pure by the criteria of gel electrophoresis and ultracentrifugation, contains approx. 70% of the chlorophyll a of the organism. Studies of the composition of the complex indicate that the protein moiety is probably made up of subunits (mol. wt. 35000), each of which contains five moles of chlorophyll and a trace of β-carotene and echinonone. 2. 2. Comparison of the physical and chemical properties of the algal chlorophyll-protein complex with those of a water-soluble bacteriochlorophyll-protein of green bacteria, and another detergent-soluble chlorophyll a-protein complex of higher plants suggests that all photosynthetic organisms might contain an analogous class of chlorophyll-proteins (mol. wt. 150000-160000), which are associated with photo-chemical system I activity, and which are composed of four identical protein subunits and 20 moles of chlorophyll. 3. 3. The water insolubility of the algal and higher plant chlorophyll-protein complexes is most probably explained by the presence of apolar amino acid residues on the surface of the molecule. In vivo the chlorophyll a-proteins are postulated to be attached to the lamellar membrane by hydrophobic bonding of the apolar regions to the lamellar lipids. 4. 4. Comparative studies indicate that the algal and higher plant complexes are much more closely related to each other than to the bacterial complex. © 1960.