Photosynthetic carbon metabolism.

Early in this century, it was thought that photochemical decomposition of carbon dioxide gave oxygen and reduced carbon (1). In 1931, van Niel (2) formulated photosynthesis as a transfer of hydrogen from water to carbon dioxide inn higher plants, and from other hydrogen donors to carbondioxide in photosynthetic bacteria. The photochemical decomposition of water to give oxygenl received further support when Hill and Scarisbrick (3) found that illuminated chloroplasts evolve oxygen when supplied with a suitable electronm acceptor. Then, in 1941, Ruben and coworkers (4) showed that oxygen evolved during photosynthesis agreed in isotopic composition with the oxygen of water rather than with that of carbon dioxide. With the discovery of radiocarbon, Rubenand coworkers (5, 6) could prove that the fixation of carbon dioxide proceeds in the dark to an intermediate compound, which is subsequently transformed in the light.