d-
Galactosone (d-lyxo-2-hexosulose) is phosphorylated and metabolized to the
uridine diphosphate derivative in AS-30D
hepatoma cells and rat liver. These reactions were catalysed in vitro by
galactokinase and hexose-1-phosphate uridylyltransferase.
Nucleotide analyses by high-performance liquid chromatography and enzymic assays revealed that this
galactose analogue interferes with cellular
pyrimidine nucleotide metabolism leading to a deficiency of
UTP. [(14)C]
Uridine labelling of
hepatoma cells indicated a division of [(14)C]uridylate from
UTP into
UDP-
galactosone; the latter was formed at a rate of more than 1.7mmolxh(-1)x(kg AS-30D or liver wet wt.)(-1). As a consequence of
UTP deficiency, d-
galactosone (1mmol/1 or 1mmol/kg body wt.) strongly enhanced the rate of
pyrimidine synthesis de novo as evidenced by incorporation of (14)CO(2) into uridylate and by an expansion of the uridylate pool. This resulted in a doubling of the total
acid-soluble uridylate pool within 70min in the
hepatoma cells and within 110min in rat liver. Combined treatment of
hepatoma cells with d-
galactosone and
N-(phosphonoacetyl)-l-aspartate, an inhibitor of
aspartate carbamoyltransferase, prevented the expansion of the uridylate pool and led to a synergistic reduction of
UTP to 10% of the content in control cells. Hepatic
UTP deficiency was selective with respect to other
nucleotide 5'-triphosphates but was associated with reduced contents of
UDP-glucose,
UDP-
glucuronate, and
UDP-N-acetylhexosamines. Isolation of the
UDP derivative of d-
galactosone revealed an extremely
alkali-labile
UDP-
sugar, probably an isomerization product of
UDP-
galactosone, that was degraded by elimination of
UDP with a half-life of 45min at pH7.5 and 37 degrees C. The instability of
UDP-
galactosone may contribute in vivo to limit the time period of severe
uridine phosphate deficiency in addition to the compensatory role of
pyrimidine synthesis de novo. During the initial time period, however, d-
galactosone is effective as a powerful uridylate-trapping
sugar analogue.