Jehoon Yang1,2, Su Xu1, Jun Shen3
1NIMH, USA; 2Samsung
Biomedical Research Institute, Korea; 3NIMH, Bethesda, MD, USA
13C MRS has been applied to studying brain metabolism by measuring 13C label incorporation into cytosolic pools. The rate of 13C label exchange between mitochondria and cytosolic glutamate and aspartate (Vx) has been controversial. Because brain fumarase is exclusively located in the mitochondria it is possible to directly measure Vx from the four-carbon side of the tricarboxylic acid cycle (TCA) by saturation transfer. In rat brain a 13C saturation transfer effect on aspartate C2 was detected after extensive signal averaging with fumarate C2 irradiated using radiofrequency pulses. Quantitative analysis found that Vx >> the TCA cycle rate.