Homozygotes exhibit little or no activity of four
molybdenum hydroxylases, i.e., 25% normal levels of xanthine
dehydrogenase (XDH) activity (Keller and Glassman), 12% normal
aldehyde oxidase (AO) activity (Courtright, 1967, Genetics
57: 25-39), no pyridoxal oxidase (PO) (Keller and Glassman)
and 5-10% normal levels of sulfite oxidase (SO) (Bogaart and
Bernini, 1981, Biochem. Genet. 19: 929-46) (2% according to
Schott, Baldwin and Finnerty). Residual activity of AO and
XDH thermolabile (Schott, Baldwin and Finnerty). These
reduced activities not accompanied by comparable reductions in
the levels of crossreacting material (CRM) indicating that the
structural genes for the enzymes are still being expressed
(Glassman, Shinoda, Duke, and Collins, 1968, Ann. N.Y. Acad.
Sci. 151: 263-73; Browder, Wilkes, and Tucker, 1982, Biochem.
Genet. 20: 111-24 and 125-32; Warner, Watts, and Finnerty,
1980, Mol. Gen. Genet. 180: 449-53). lxd+ postulated to be
involved in production of an enzyme cofactor (Glassman et al.,
1968); dietary molybdenum shown to increase specific activity
of AO and XDH in flies homozygous for some, but not all, lxd
alleles (Duke, Rushing, and Glassman, 1975, Biochem. Genet.
13: 53-64). lxd homozygotes shown to have only 10% normal
molybdenum cofactor activity (Schott, Baldwin, and Finnerty).
Tungsten, a known antagonist of molybdemum cofactor, shown to
mimic lxd in wild type (Warner and Finnerty, 1981, Mol. Gen.
Genet. 184: 92-96) and to exacerbate the effects of lxd
(Bentley, Williamson, and Oliver, 1981, Can. J. Genet. Cytol.
23: 597-609). The maternal effects of cin and mal are
suppressed in cin lxd and mal lxd offspring of cin/+ and mal/+
mothers respectively; dietary molybdenum counteracts the
suppression; lxd also suppresses complementation between various pairs of partially complementing mal alleles (Courtright,
1975, Mol. Gen. Genet. 142: 231-38). Dietary tungsten produces brown eye color in lxd flies, which normally have red
eyes; used to select new lxd alleles (Bentley, Williamson, and
Oliver); allopurinol used in the same way (Schott, Baldwin,