Randomization of carbon atoms in the glucose molecule and changes of specific radioactivity of14CO2 liberated by the callus tissue ofDaucus carota L. from glucose-6- and -1-14C

On incubation of the callus tissue of Daucus carota L. in solutions of glucose-6- 14 C and -1- 14 C the distribution of radioactivity in the molecule of endogenous glucose will change and the ratio of activities of liberated 14 CO 2 (C 6 /C 1 ) will rise The limits of possible changes of specific activity of 14 CO 2 and of the C 6 /C 1 ratio were calculated with respect to the observed randomization and it was shown that the mutual exchange of carbon atoms in the molecules is not the decisive cause of the rise of the ratio. The specific radioactivity of 14 C in CO 2 is as much as 12 times higher than that of endogenous glucose and fructose and about twice as high as the theoretical maximum. This might indicate that in addition to the cytoplasmic fraction of glucose the callus cells contain a fraction of low metabolic activity, most likely in the vacuoles, that could account for some of the increase of the C 6 /C 1 value. The main reason for the changes in the C 6 /C 1 ratio is envisaged in the establishment of isotopic equilibrium between the pentose cycle and glycolysis and other metabolic systems, in particular via triose phosphates, the radioactivity of which can greatly affect the C 6 /C 1 ratio, as was shown in a model experiment.