14CO2-

Microbiological procedures which exploit the ability of bacteria and photosynthetic algae to incorporate exogenous labeled precursors such as 14CO2, SO%, and 32pQ3- [ can be used to label complex molecules in cells such as proteins (qv) and nucleic acids (qv), which are then processed to give labeled constituents such as uniformly labeled C-amino acids, C-nucleotides, C-fipids, LS-amino acids, etc (8). 

Formation of the enediol(ate) of RuBP is readily assayed on the basis of exchange of solvent protons with the C3 proton of substrate (20-22). The six-carbon intermediate of the carboxylation pathway (II in Fig. 1) can be prepared by rapid quench after mixing equimolar amounts of RuBP and the carboxylase in the presence of 14CO2 (23). Availability of this labeled intermediate allows determination of an enzyme s commitment to forward processing in the carboxylation step. Decomposition, via decarboxylation, is observed as a decrease in radioactivity that can be stabilized by borohydride, whereas forward catalysis is equated with an increase in acid-stable radioactivity. 

Miinnich (1963) 14co2 <1 From difference in the increase of bomb-produced l4C in both hemispheres... 

Lai and Rama (1966) 14co2 1.2 0.8 0.3 From tropospheric increase of bomb-produced 14C injected from the stratosphere... 

Young and Fairhall (1968) 14co2 1.5 From stratospheric inventory change with time... 

The carbon-14 atoms react with oxygen molecules to form " C02 - This process continually supplies the atmosphere with radioactive C02, which is removed from the atmosphere by photosynthesis. The intensity of cosmic rays is related to the sun s activity. As long as this remains constant, the amount of C02 in the atmosphere remains constant. 14CO2 is incorporated into living organisms just as ordinary i C02 is, so a certain fraction of all carbon atoms in living substances is carbon-14. This decays with a half-life of 5730 years. 

---