Abstract
Xanthine dehydrogenase (XDH) catalyzes oxidation of hypoxanthine and xanthine to uric acid, which makes silkworm larval skin opaque. The silkworm, Bombyx mori, has two XDH isozymes (XDHα and XDHβ) and two XDH genes (BmXDH1 and BmXDH2). The BmXDH1 gene has been shown to be identical to the oq gene, whose mutation inactivates XDHα and makes larval skin translucent. Thus, BmXDH1 is the XDHα gene, and BmXDH2 is hypothesized to encode XDHβ. In order to test the hypothesis, XDH isozymes were analyzed by Western blotting with antibodies against BmXDH1 and BmXDH2. Both antibodies immunoreacted with bands of expected sizes in normal silkworms but BmXDH1 was not detected in the oq mutant. Since the mutant expresses BmXDH1 (oq) mRNA, this result suggests that BmXDH1 translation is suppressed in the mutant, which has an 8-bp deletion in the BmXDH1 (oq) gene resulting in a premature stop codon. BmXDH2 protein was detected both in oq/oq and +/+ fat body. Western blotting with anti-BmXDH2 antibody also showed that XDHβ is BmXDH2 because they have same electrophoretic mobility on native PAGE.
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