Xanthine dehydrogenase from Drosophila melanogaster: a comparison of the kinetic parameters of the pure enzyme from two wild-type isoalleles differing at a putative regulatory site.

Xanthine dehydrogenase (XDH) from Drosophila melanogaster has been purified to homogeneity by immunoaffinity chromatography, and its kinetic parameters determined. Drosophila XDH exhibits ordered binding for substrate and NAD+, analogous to the corresponding enzymes from vertebrate sources. The wild-type enzyme exhibits a Km for xanthine of 2.4 X 10(-5) M, and for NAD+ of 4.0 X 10(-5) M. XDH purified from a genetic variant exhibiting elevated levels of enzyme activity has similar kinetic constants. The results provide further evidence that the site of variation in the latter strain results in higher steady state numbers of XDH molecules per fly.