Article

Orientation-conserved transfer of symmetric Krebs cycle intermediates in mammalian tissue.

Department of Chemistry, University of Texas at Dallas, Richardson 75083-0688.
Biochemistry (impact factor: 3.42). 06/1994; 33(20):6268-75. pp.6268-75
Source: PubMed

ABSTRACT Metabolism of [2-13C]-, [3-13C]-, and [1,2,3-13C]propionate in perfused rat livers and [2-13C]-acetate in perfused rat hearts has been examined in tissue extracts by 13C NMR. Label from [2-13C]-propionate was preferentially incorporated into the C2 carbon of lactate, alanine, and aspartate in liver tissue while label from [3-13C]propionate appeared preferentially in the C3 carbon of those same molecules. These data suggest that 13C may not be completely randomized in the symmetric citric acid cycle intermediates succinate and fumarate as is normally assumed but that some fraction of those intermediates may be transferred between enzymes in this span of the cycle with conservation of spatial orientation, consistent with recent results obtained in yeast [Sumegi et al. (1990) Biochemistry 29, 9106-9110]. This was confirmed by performing similar experiments with [1,2,3-13C]propionate. Time-dependent asymmetry was also observed between the intensities of the glutamate C2 and C3 resonances and between the aspartate C2 and C3 resonances in 13C NMR spectra of intact hearts and heart extracts during early perfusion with [2-13C]-acetate. A model is presented which predicts that isotopic asymmetry is observed only during the first 2-3 turns of the cycle pools when isotope enters the cycle via acetyl-CoA even if all symmetric cycle intermediates retain a unique molecular orientation on each pass through the citric acid cycle.

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    Article: Central carbon metabolism of Saccharomyces cerevisiae explored by biosynthetic fractional (13)C labeling of common amino acids.
    H Maaheimo, J Fiaux, Z P Cakar, J E Bailey, U Sauer, T Szyperski
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    European Journal of Biochemistry 05/2001; 268(8):2464-79. · 3.58 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

alanine
 
aspartate C2
 
C2 carbon
 
C3 carbon
 
C3 resonances
 
citric acid cycle
 
enzymes
 
first 2-3
 
glutamate C2
 
intact hearts
 
isotopic asymmetry
 
lactate
 
preferentially
 
recent results
 
similar experiments
 
spatial orientation
 
symmetric citric acid cycle intermediates succinate
 
symmetric cycle intermediates
 
Time-dependent asymmetry
 
unique molecular orientation