The Path of Carbon in Photosynthesis

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Abstract
The rates of the photosynthetic and dark fixations of C14O2 in Scenedesmus have been compared in dilute phosphate buffers ranging from pH 1.6 to pH 11.4 and the amounts of carbon incorporated into the various products have been determined by means of the radiochromatographic method. In photosynthesis, an acid medium favours early incorporation of C14 into sucrose, polysaccharides, and the three-carbon compounds alanine and serine. Fixation into the four-carbon compounds malic and aspartic acids is enhanced in an alkaline medium. Kinetic experiments at several pH values suggest that several paths may be available for carbon dioxide assimilation. A tentative correlation of the results with the pH optima of some enzymes and resultant effects upon concentrations of intermediates is presented.