The Path of Carbon in Photosynthesis

Although the overall reaction of photosynthesis can be specified with some degree of certainty (COs + H~O + light ~ sugars + possibly other re-duced substances), the intermediates through which the carbon passes during the course of this reduc-tion have, until now, been largely a matter of con-jecture. The availability of isotopic carbon, that is, a method of labeling the carbon dioxide, provides the possibility of some very direct experiments de-signed to recognize these intermediates and, perhaps, help to understand the complex sequence and inter-play of reactions which must constitute the photo-chemical process itself. The general design of such experiments i an obvious one, namely the exposure of the green plant atic investigation are given in Table I which in-eludes three sets of experiments, namely a dark fixation experiment and two photosynthetic experi-ments, one of 30 seconds duration and the other of 60 seconds duration. The method that was developed for separating the various components of the cell is shown in diagrammatic form in Figure 1. Six fractions were obtained, and on the basis of the method of frac-tionation, certain general properties of the com-pounds contained in each of these fractions can be specified. The insoluble fraction, which contained practi-cally none of the very quickly formed radioactive products, consists of the high molecular weigh