Isotopic methods for probing organization of cellular metabolism

Abstract

These examples serve to illustrate that it is now possible to investigate metabolism in intact tissues using a variety of biophysical methods. While we have concentrated on NMR methods, reflecting our own interests in using 13C as a metabolic tracer, GC-mass spectroscopy can often provide similar metabolic information and has the advantage of increased sensitivity over NMR. Combining either or both of these technologies with cleaver 'chemical biopsy' methods offers new opportunities to examine what may seem to be old metabolic questions in a much more relevant environment, the native state.

Measurement of gluconeogenesis and pyruvate recycling in the rat liver: a simple analysis of glucose and glutamate isotopomers during metabolism of [1,2,3‐13C3]propionate

“…This observation, confirmed here, was interpreted as evidence for incomplete randomization of symmetric 4 carbon citric acid cycle intermediates [21]. Subsequently, we pointed out that this multiplet pattern could also be observed whenever pyruvate recycling was significant [29]. In these earlier reports the conclusions were solely based on the enrichment patterns detected in gluconate C2, aspartate C2 or lactate C2 (each reflecting the C2 carbon of OAA) and this did not provide sufficient information to distinguish between pyruvate recycling or orientation conserved transfer.…”

Central carbon metabolism of Saccharomyces cerevisiae explored by biosynthetic fractional 13C labeling of common amino acids

“…Calculation of X exch according to assumes complete symmetrization of 13 C labeling patterns about the C2‐C3 bond of succinate or fumarate [1] arising from unrestricted rotation in solution. In cases where metabolite channeling [53–57], which may restrict rotational reorientation, had to be invoked for the exchange reaction, the value for X exch would represent a lower bound (see below).…”

Relative rates of anaplerotic flux in rested and contracted rat skeletal muscle measured by 13C NMR spectroscopy

“…13 C magnetic resonance spectroscopy (MRS) techniques allow calculation of relative flux rates through multiple pathways as well as permitting detection of successive biochemical events (Sherry & Malloy, 1996). Analysis of the 13 C isotope isomers (isotopomers) of glutamate has been central in the development of complex analysis models for calculating TCA cycle flux and the rate of flux through anaplerotic pathways (Sherry & Malloy, 1998).…”