Abstract
The alpha-amylase in Drosophila melanogaster is a highly polymorphic enzyme, at both the allozyme level and the specific activity level. This enzyme changes its specific activity drastically depending on both food conditions and developmental stages, and it has been suggested that the ability to change its activity depending on the source of food has positive correlation with fitness. But the cause of the difference of specific activity among strains and food compositions is not known. In order to investigate the cause of these differences, we measured both the specific activity of amylase and the relative amount of Amy mRNA in eight strains of D. melanogaster with different electromorphs, in two food environments and two developmental stages. We found the following. First, the food-dependent activity change is regulated at the transcription level. Second, there was a significant correlation between specific activity and mRNA level among strains. So 80 to 90% of the specific activity difference can be explained by differences in the level of mRNAs, but the remaining part cannot. Finally, there were significant differences in specific activity per mRNA both among strains and between developmental stages. This suggests that there are differences in the catalytic efficiency of each allozyme, strain- or stage-specific translation rate, enzyme stability, or differential use of two Amy loci.
