Anomeric specificity of D-glucose production by rat hepatocytes

The anomeric specificity of D-glucose metabolism in intact hepatocytes remains a matter of debate. This issue was further investigated in the present study, which is based on the quantification of the alpha- and beta-anomers of the 13C-enriched isotopomers of D-glucose generated by rat liver cells exposed to either D-1-13C] fructose or D-2-13C] fructose in the presence of D2O. The D-1-13C]glucose/D-6-13C]glucose paired ratios found in the cells exposed to D-1-13C] fructose and the D-2-13C]glucose/D-5-13C]glucose paired ratios found in the cells exposed to D-2-13C] fructose yielded a paired beta/alpha ratio averaging (mean +/- S.E.M.) 79.3 +/- 6.1%. In the case of the isotopomers of D-glucose formed by gluconeogenesis, the D-2-13C]glucose/D-5-13C]glucose and D-3-13C]glucose/D-4-13C]glucose paired ratios found in cells exposed to D-1-13C] fructose, as well as the D-1-13C]glucose/D-6-13C]glucose and D-3-13C]glucose/D-4-13C]glucose paired ratios found in cells exposed to D-2-13C]fructose, yielded an alpha/beta paired ratio averaging 75.0 +/- 5.8%. Last, in the cells exposed to D-2-13C]fructose, the beta/alpha ratio for the C2-deuterated isotopomers of D-2-13C]glucose represented 78.9 +/- 3.7% of that for the C5-deuterated isotopomers of D-5-13C]glucose. The three values representative of the anomeric specificity of D-glucose production by liver cells were not significantly different from one another, with an overall mean value of 76.9 +/- 3.6%. These findings unambiguously document that the anomeric specificity of phosphoglucoisomerase is operative in intact hepatocytes, resulting in a preferential output of the alpha-anomer of 13C-enriched D-glucose under the present experimental conditions.