Biochemistry 462
Intact, isolated chloroplasts are useful in the studies of photosynthesis carbon metabolism. Metabolites such as the triose phosphate (glyceraldehydes 3-phosphate and dihydroxyacetone 3-phosphate) can be added to the medium containing the isolated chloroplasts. The triose phosphates are taken up in exchange for the organic phosphate (Via the Pi: triose phosphate translocator in the chloroplast envelope membrane) and subsequently metabolized.
In one such experiment glyceraldehydes 3-phosphate, 90% enriched with carbon 13 in the aldehydic carbon, was added to the suspension of the intact chloroplast in the light and in the presence of CO2-free air. Under such conditions glycolate accumulated in the external medium. The glycolate was purified and subjected to mass spectrometric analysis as glycolic acid (nominal mass=76) with the following result.
m/e Relative intensity
76 0.67
77 0.06
78 0.27
Explain this result!