galactose1phosphate

Galactose-1-phosphate, also written as galactose-1-phosphate and abbreviated Gal-1-P, is a phosphorylated derivative of the sugar galactose and a key intermediate in the Leloir pathway of galactose metabolism. It is produced when galactose is phosphorylated by galactokinase, using ATP as a phosphate donor.

In the principal sequence of reactions, galactose-1-phosphate is converted by galactose-1-phosphate uridylyltransferase (GALT) in a transfer reaction that uses UDP-glucose as the uridylyl donor. This step yields UDP-galactose and glucose-1-phosphate. Glucose-1-phosphate can then be converted to UDP-glucose by UDP-glucose pyrophosphorylase, allowing the cycle to continue or to supply substrates for biosynthetic processes. UDP-galactose serves as a donor for the synthesis of lactose in mammary tissues and for the formation of various glycoproteins, glycolipids, and proteoglycans.

Clinical significance of galactose-1-phosphate centers on defects in the GALT enzyme. Classic galactosemia results from GALT deficiency and leads to accumulation of galactose-1-phosphate and related metabolites, with potential toxicity to the liver, nervous system, and ocular tissues, especially in newborns. Management in affected individuals typically involves dietary restriction of galactose to reduce metabolite buildup, and monitoring through newborn screening programs and clinical follow-up.

See also: Leloir pathway; galactokinase; GALT; UDP-glucose pyrophosphorylase; UDP-galactose.