ABSTRACT
The relationship between sulfite oxidase (SO) and sulfite sensitivity in Drosophila melanogaster is addressed. Significant improvements to the SO assay have provided an investigative tool which can be applied to further studies of this molybdoenzyme. Using the second-instar larval stage of D, melanogaster, we have shown a direct relationship between measured levels of sulfite oxidase activity and the organism's ability to withstand a sulfite challenge. Implementation of a sulfite-testing procedure confirmed the documented instability of sulfite in solution and may explain some of the conflicting results reported in the SO literature. Results of the tungstate-addition experiments confirm that Drosophila SO is a molybdoenzyme and its activity was shown to be governed by three of the four loci known to affect more than one molybdoenzyme. The ability of D. melanogaster to withstand the application of exogenous sulfites is shown to be dependent on sulfite oxidase activity.
Subject(s)
Drosophila melanogaster/drug effects , Drosophila melanogaster/enzymology , Oxidoreductases Acting on Sulfur Group Donors/metabolism , Sulfites/pharmacology , Animals , Drosophila melanogaster/genetics , Female , Larva , Male , Oxidoreductases Acting on Sulfur Group Donors/geneticsABSTRACT
Mutation at the aldox-2 locus in Drosophila melanogaster affects the specific activities of four molybdoenzymes differentially during development. Sulfite oxidase activity is normal during late larval and pupal stages but is reduced during early adult stages in aldox-2 organisms. There was complete concordance among the effects of aldox-2 on sulfite oxidase, aldehyde oxidase, xanthine dehydrogenase, and pyridoxal oxidase, when 38 stocks were analyzed which were derived from single recombination events between c and px, markers which flank aldox-2. Several different biochemical analyses indicate that the active molybdoenzymes present in the aldox-2 strain are normal with respect to size, shape, pH-activity profile, Km, and molecular weight. Significant differences were found between the aldox-2 strain and the OR control strain in their responses to dietary Na2MoO4 and Na2WO4. The mutant strain is much more resistant to the effects of dietary Na2WO4 and much more responsive to the administration of Na2MoO4 than the OR control strain when these effects are quantitated by measurements of molybdoenzyme specific activities. This evidence suggests that the aldox-2+ gene product has a molybdenum binding site which can also bind tungsten and that this site is altered in the mutant strain. The hypothesis presented explains the observed effects of the aldox-2 mutation and relates them to the other mutations reported in this gene-enzyme system.
