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 C-13-enriched isotopomers of D-glucose generated by rat liver cells exposed to either D-[1-C-13] fructose or D-[2-C-13] fructose in the presence of D2O. The D-[1-C-13]glucose/D-[6-C-13]glucose paired ratios found in the cells exposed to D-[1-C-13] fructose and the D-[2-C-13]glucose/D-[5-C-13]glucose paired ratios found in the cells exposed to D-[2-C-13] 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-C-13]glucose/D-[5-C-13]glucose and D-[3-C-13]glucose/D-[4-C-13]glucose paired ratios found in cells exposed to D-[1-C-13] fructose, as well as the D-[1-C-13]glucose/D-[6-C-13]glucose and D-[3-C-13]glucose/D-[4-C-13]glucose paired ratios found in cells exposed to D-[2-C-13]fructose, yielded an beta/alpha paired ratio averaging 75.0 +/- 5.8%. Last, in the cells exposed to D-[2-C-13]fructose, the beta/alpha ratio for the C-2-deuterated isotopomers of D-[2-C-13] glucose represented 78.9 +/- 3.7% of that for the C-5-deuterated isotopomers of D-[5-C-13]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 a- anomer of C-13-enriched D-glucose under the present experimental conditions.