Interconversion of Isoenzymes of Drosophila Alcohol Dehydrogenase

Drosophila alcohol dehydrogenase and its subunits were examined for their physical characteristics. The intact enzyme was shown to have a molecular weight of approximately 60,000. The smallest apparent subunit was obtained by dissociating the enzyme with sodium dodecylsulfate and the molecular weight obtained was 7,500. Evidence for three partially dissociated forms was obtained; the subunits obtained by urea treatment was 25,000 to 30,000 daltons, the subunits obtained by treatment with maleic anhydride had an apparent molecular weight of 15,000 daltons, and the subunits obtained by the addition of urea and sodium dodecylsulfate together gave molecular weights of 30,000, 22,500, 15,000, as well as 7,500. Dissociation by sodium dodecylsulfate alone (no urea) produced subunits of 7,500 daltons. Therefore we propose that Drosophila alcohol dehydrogenase is composed of eight subunits. These are the smallest subunits of an enzyme reported to date. The size of the subunit conflicts with genetic and analytical data presented previously. The intact enzyme can occur in five or more electrophoretic forms. Evidence is presented to show that these forms do not represent dimers or aggregates since they all have the same sedimentation rates.