Multiple molecular forms of xanthine dehydrogenase and related enzymes

The molybdoenzyme system of Drosophila melanogaster. I. Sulfite oxidase: identification and properties. Expression of the enzyme in maroon-like (mal), low-xanthine dehydrogenase (lxd), and cinnamon (cin) flies

Sulfite oxidase (sulfite: ferricytochrome c oxidoreductase; EC 1.8.2.1) has been detected in Drosophila melanogaster and some of its properties have been studied. In most respects this enzyme resembles the mammalian sulfite oxidases except for its molecular weight (148,000), which is somewhat higher than that of rat sulfite oxidase (116,000). Cytochrome c, potassium-ferricyanide, and oxygen can serve as electron acceptors in the oxidation of sulfite by the enzyme. Although definite evidence can be obtained only through the analysis of the pure enzyme, experiments involving tungstate feeding suggest that Drosophila sulfite oxidase is most probably a molybdoenzyme. Extracts of mal flies show normal levels of sulfite oxidase, whereas lxd flies have only 5-10% of the activity of wild type, and in cin flies the enzyme is apparently absent. While it is possible that the lxd and cin mutations are at some level responsible for the defective synthesis of a molybdenum-containing cofactor (supposed to be present in most molybdoenzymes), the evidence accumulated so far by several authors and the results of the present investigation argue against the involvement of a Mo cofactor in the multiple enzyme deficiencies observed in mal flies.

Gene regulation in Drosophila: independent expression of closely linked, related structural loci

A number of biochemical and genetic features shared by aldehyde oxidase and pyridoxal oxidase in Drosophila melanogaster indicate a close relationship between these enzymes. The present work shows that probable structural genes for these enzymes are within about 0.08 map unit of each other. Comparison with intensively studied regions of the genome suggests that this value is of the order of magnitude expected for adjacent functional units. Despite this close linkage, there is no indication of coordinate expression of the two enzymes. These results are consistent with the idea that each structural gene is under control of its own regulatory region, but alternative explanations are possible.