Effect of Dietary Carbohydrates on the Expression of GPDH Isozymes in Drosophila melanogaster

Abstract

We have examined the relative effects of dietary carbohydrates on GPDH isozymes in both larvae and adults of Drosophila. In larvae, GPDH tissue activities and cross-reacting materials (CRMs) were significantly increased in proportion to the dietary carbohydrate concentration. These observations indicate that the diet-induced change in GPDH activity is due to the modulation of GPDH CRM. The carbohydrate-stimulated increase of GPDH in larvae appears to be involved with the function of larval isozyme, GPDH-3, which plays a role in the diversion of carbohydrate into lipid. GPDH activities and CRMs in adult flies were a little increased with increasing carbohydrate concentration, but the staining activity in CRMs was reduced by high concentration of carbohydrate. In the case of adults, the exact modulating effects on functionally distinct GPDH isozymes are hard to discern in the protein level, because all the isozymes are present at the adult stage. With respect to transcript abundance, Northern analysis showed that Gpdh-411 transcript, encoding adult-limited GPDH-1, was repressed in high-carbohydrate diet. The change in GPDH-1 appears, in part, to be a stressful response to a high-carbohydrate diet. As a result, these findings suggest that GPDH isozymes can respond to dietary carbohydrates to varying degrees, and the regulation of isozymes by the diet is possibly involved with tissue-specific functions.