DETERMINATION OF C-13 ENRICHMENT AT SPECIFIC POSITIONS OF PLASMA-GLUCOSE BY GAS-CHROMATOGRAPHIC MASS-SPECTROMETRIC ANALYSIS OF THE 1,2 5,6-DIISOPROPYLIDENE-3-O-ACETYL-ALPHA-FURANOSYL DERIVATIVE/

To determine C-13 enrichment at specific positions of glucose, plasma samples (50-100 mu l) were deproteinized using ethyl alcohol, centrifu ged, and evaporated to dryness, and the residues were derivatized with acetone/H2SO4 (100/1, v/v). After acetylation, the ,2:5,6-diisopropyl idene-3-O-acetyl-alpha-furanosyl derivative was analyzed by gas chroma tography-mass spectrometry. The method was tested using mixtures of na tural and C-13-labeled glucose molecules. Ions at m/z 113, 114 143, 14 4, 287, and 288, corresponding to the C-2-C-4, C-1-C-4, and C-1-C-6 pa rts of natural or C-13-labeled glucose molecule, respectively, were se lectively monitored to determine the C-13 content of these fragments. This method was applied to the study of plasma glucose-labeling patter n following the infusion of [3-C-13]lactic acid at tracer doses. Assum ing equilibration of label through triose-phosphate isomerization in v ivo, we determined the C-13 enrichment of carbons 1, 2, and 3 of gluco se; the values for E(1)/E(3) and E(2)/E(1) ratios of 8.1 and 0.77, res pectively, are consistent with those obtained in studies using radioac tive tracers. (C) 1994 Academic Press, Inc.