Changes in protein turnover after heat shock are related to accumulation of abnormal proteins in aging Drosophila melanogaster.

Adult Drosophila melanogaster kept at 24 degrees C show a progressive decline in the synthesis and degradation of proteins with age. After exposure of young, 7-10 days old flies to 20 min of heat shock at 37 degrees C, the incorporation of [35S]-methionine into trichloroacetic acid precipitable proteins decreases to more than 60% of that observed in non-stressed flies. This decrease is also accompanied by a lower protein degradation rate. In contrast, the same stress in old, 49 days old insects results in a 3-fold increase in protein synthesis as compared to either non-heat shocked senescent flies or to young heat-shocked flies. The older flies also have faster protein turnover than unshocked controls. An effect similar to that observed in senescent Drosophila also occurs in young flies that have been fed canavanine, an arginine analogue, before and during heat shock. These results suggest that an age dependent accumulation of abnormal proteins may be responsible for the changes in protein turnover observed in the heat-shocked old flies.