Biochemical characterization of the products of the Adh loci of Drosophila mojavensis.

The electrophoretic pattern of alcohol dehydrogenase (ADH) of Drosophila mojavensis is composed of multiple bands. In previous studies from this laboratory we suggested on the basis of genetic evidence that multiple ADH bands were due to the presence of a gene duplication. In the studies presented here, this hypothesis is supported by data derived from comparing the protein biochemistry of each ADH. Three forms of D. mojavensis ADH have been isolated. These are the ADH-1 homodimer, the ADH-2 homodimer, and the ADH-1 ADH-2 interlocus heterodimer. Each of these isozymes has a native molecular weight of approximately 50,000. Each native molecule is composed of two subunits of identical size, 24,000 daltons. The native molecules differ slightly in their isoelectric points. Thermal denaturation also reveals that ADH-1 and ADH-2 are slightly different, ADH-1 being somewhat more thermostable. The interlocus heterodimer has properties intermediate between those of ADH-1 and those of ADH-2. Kinetic comparison also indicates a similarity among the three isozymes. ADH-2 is somewhat better at oxidizing ethanol relative to 2-propanol as compared to ADH-1. All of our studies support the general conclusion that the isozymes of ADH found in D. mojavensis are similar to one another and to other ADH from other species of Drosophila. This supports our hypothesis that multiple bands of ADH in D. mojavensis reflect the presence of a duplication of the Adh locus in that species.