19F and 13C NMR studies of polyol metabolism in freeze-tolerant pupae of Hyalophora cecropia

Sorbitol biosynthesis and regulation in freeze tolerant pupae of Hyalophora cecropia have been investigated as a function of temperature by 19F and 13C nuclear magnetic resonance (NMR) spectroscopy using several 13C-labeled and/or fluorine-substituted carbohydrates. 3-Deoxy-3-fluoro-D-glucose (3DFG) was metabolized to 3-deoxy-3-fluoro-D-sorbitol (3DFS), 3-deoxy-3-fluoro-D-fructose (3DFF), and 3-deoxy-3-fluoro-D-gluconic acid (3DFGA), indicating that the enzymes required for sorbitol biosynthesis and metabolism are active in H. cecropia at warm (22 degrees C) and cold (4 and -10 degrees C) temperatures. Two additional metabolites were produced when pupae were injected with either 3DFG, 3DFS, 3DFF, or 3-deoxy-3-fluoro-D-mannose (3DFM). One of these was identified as 3-deoxy-3-fluoro-D-mannitol (3DFML) by 13C NMR using [1-13C]3DFM and [1-13C]3DFG as metabolic probes. H. cecropia pupae injected with D-glucose labeled with 13C at C-1, C-2, or C-3 and subsequently analyzed by 13C NMR clearly demonstrated the ability to generate sorbitol and fructose. In contrast, gas chromatography/mass spectrometric analysis of hemolymph failed to detect sorbitol in pupae reared under natural conditions (i.e. in the absence of injected enriched sugars). Thus, although H. cecropia pupae have the enzymic machinery to biosynthesize sorbitol, they do not appear to accumulate high steady-state concentrations of this polyol over the temperature range studied. The specificity of the enzymes involved in alditol biosynthesis in H. cecropia was examined by 13C NMR with a wide range of aldoses enriched with 13C at C-1. Pupae were capable of converting these sugars to their corresponding [1-13C]alditols, indicating that nonspecific dehydrogenase(s), in addition to aldose reductase, is(are) involved in polyol biosynthesis in H. cecropia pupae.