The Path of Carbon in Photosynthesis

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.