PHYSICAL AND CHEMICAL CHARACTERISTICS OF CHLOROPLAST FRAGMENTS. APPLIED RESEARCH CONCERNING ARTIFICIAL PHOTOSYNTHESIS

Chloroplasts isolated from spinach leaves were physically fragmented and then fractionated by differential centrifugation. A high-activity fraction, designated CF(20-50), was obtained and retained its high activity regardless of environmental changes. It had a low protein content and a relatively high chlorophyll-to-protein ratio. Plastoquinone was present in high concentration. Extraction of plastoquinone from CF(20-50) inhibited Hill activity. Unlike whole chloroplasts, readdition of plastoquinone failed to induce even partial recovery. The average particle size in CF(20-50) was 1500 angstroms in diameter. The average sedimentation constant was 800; the molecular weight was about 8 x 10 to the 7th power; and it showed three electrophoretic bands. CF(20-50) showed maximal Hill activity, but was not the smallest photo-active unit studied. Although the nature of the smallest functional unit is uncertain, it is clear that a CF(20-50) particle is composed of smaller sub- units probably oriented to impart high activity to the larger composite structure.