Aldehyde dehydrogenase (ALDH) activity in Drosophila melanogaster adults: evidence for cytosolic localization

The subcellular localization of the aldehyde dehydrogenase activity from the ALDH (EC 1.2.1.3) enzyme has been studied in nutritionally manipulated Drosophila melanogaster adults from a wild (LRC) and an ADH-null (bAdhn4) strain. ALDH activities from ALDH or ADH (EC 1.1.1.1) enzymes were selectively inhibited by prefeeding respectively the flies sucrose solutions supplemented with either cyanamide or acetone respectively. ALDH, ADH (as a cytosolic marker) and succinate dehydrogenase (EC 1.3.9.1) (as a mitochondrial marker) activities were assayed in both the mitochondrial and cytosolic fractions isolated from flies subjected to each treatment. Total ALDH activity in the cytosolic fraction was found to be between five (ADH strain) and ten (ADH strain) times higher than that in the mitochondrial fraction. Prefeeding cyanamide resulted in a 64% (ADH strain) and a 90% (ADH strain) reduction of the cytosolic ALDH activity, whereas prefeeding acetone resulted in a 38% (ADH strain) reduction of this activity. Prefeeding both cyanamide and acetone resulted in a total inhibition of ALDH activity, which was also observed after an extended cyanamide treatment. In conclusion, our results support that, contrary to what occurs in larvae, in adults the ALDH activity from ALDH enzyme is mainly localized in the cytosolic fraction: about 85% in ADH+ and 90% in ADH- strains. Although larvae and adults use different ALDH activities to detoxify acetaldehyde (from ADH and ALDH enzymes, respectively) both of them are cytosolic. Reasons for these different uses are discussed in relation to the subcellular localization of ALDH activity.