Electrophoretic variants of xanthine dehydrogenase in Drosophila melanogaster II. Enzyme kinetics

Abstract

1. 1.|The activity of xanthine dehydrogenase in Drosophila melanogaster is affected by mutations at three loci: maroon-like (ma-l) on the X chromosome, and rosy (ry) and the low xanthine dehydrogenase (lxd) on the third chromosome. Previous studies on four types of naturally-occurring electrophoretic variants of xanthine dehydrogenase have shown that ry is a structural gene for xanthine dehydrogenase. 2. 2.|In the present study, kinetic analyses were carried out on these four electrophoretic variants. These include the K m 's of 2-amino-4-hydroxpyteridine, xanthine, methylene blue, and nicotinamide-adenine dinucleotide, and the K i 's of 2-amino-4-hydroxypteridine-6-carboxyaldehyde, ammeline, and 8-azaguanine. The data have shown no significant differences in the kinetic parameters of the xanthine dehydrogenase from the electrophoretic variants or from lxd. 3. 3.|The experiments of this study also indicate the possible presence of two active sites on xanthine dehydrogenase, one for purines and one for pteridines, and that pyridoxal can bind both active sites. 4. 4.|The biological significance of the electrophoretic variation is discussed in view of the present data.