Metabolic loss of deuterium from isotopically labeled glucose

The isotopically substituted molecule (6- 13 C, 1, 6, 6- 2 H 3 )glucose was evaluated to determine whether metabolic 2 H loss would prevent its use in quantitating pentose phosphate pathway (PPP) activity. PPP activity causes the C1 of glucose to be lost as CO 2 , while C6 can appear in lactate. 2 H NMR analysis of the lactate produced from this glucose can distinguish (3- 2 H)-lactate (from C1 of glucose) from (3- 13 C, 3, 3- 2 H Z )lactate (from C6 of glucose). 2 H NMR spectroscopic analysis of medium containing (4- 13 C, 1,6,6 −2 H 3 ) glucose after incubation with cultured rat 9L glioma cells suggested a 30.8 ± 2.1% PPP activity as compared with 6.0 ± 0.8% from separate, parallel incubations with (1- 13 C)glucose and (6- 13 C)glucose. Subsequent experiments with other isotopically labeled glucose molecules suggest that this discrepancy is due to selective loss of 2 H from the C1 position of glucose, catalyzed by phosphoman-nose isomerase. Failure to consider 2 H exchange from the C1 and C6 positions of glucose can lead to incorrect conclusions in metabolic studies utilizing this and other deuterated or tritiated glucose molecules.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38491/1/1910320317_ftp.pd

Measurement of unidirectional P(i) to ATP flux in human visual cortex at 7 T by using in vivo (31)P magnetic resonance spectroscopy

Taking advantage of the high NMR detection sensitivity and the large chemical shift dispersion offered by ultra-high field strength of 7 T, the effect of magnetization transfer on inorganic phosphate (P(i)) resonance during saturation of γ-ATP resonance, mediated by the ATP synthesis reaction, was observed noninvasively in the human primary visual cortex by using in vivo (31)P magnetic resonance spectroscopy. The unidirectional flux from P(i) to ATP was measured by using progressive saturation transfer experiments. The cerebral ATP synthesis rate in the human primary visual cortex measured by (31)P magnetic resonance spectroscopy in this study was 12.1 ± 2.8 μmol ATP/g per min, which agreed well with the value that was calculated indirectly from the cerebral metabolic rate of glucose consumption reported previously