Metabolism of glucose and mannose anomers in pancreatic islets

The alpha-anomers of D-glucose and D-mannose stimulate insulin release more efficiently than the corresponding beta-anomers. This coincides with higher glycolytic and oxidative fluxes in pancreatic islets exposed to alpha- than to beta-anomers. This situation may be attributable, in the case of alpha-D-glucose, not solely to the alpha-stereospecificity of phosphoglucose isomerase but also to that of phosphoglucomutase resulting in a higher islet content of glucose-1,6-bisphosphate, an activator of phosphofructokinase. Likewise, more aldohexose-bisphosphate accumulates in the islets exposed to alpha-D-mannose than in those incubated with beta-D-mannose. The anomeric specificity of hexose metabolism in pancreatic islets supports the fuel hypothesis for insulin release.