Galactose metabolism

Category: catabolism

Overview

Conversion of dietary galactose (primarily from lactose) into glucose-1-phosphate via the Leloir pathway. Galactose → galactose-1-P (galactokinase, GALK1) → glucose-1-P (galactose-1-P uridyltransferase, GALT — the Leloir enzyme; uses UDP-glucose as the UDP donor, regenerating UDP-galactose). Classic galactosemia = GALT deficiency: G1P accumulates, depletes phosphate + UDP, produces hepatic + renal + cerebral injury in the newborn period; lethal without lactose-free diet. Galactokinase deficiency = milder galactosemia variant with isolated cataracts. Epimerase deficiency = third variant. Newborn screening detects GALT specifically. Long-term outcomes (ovarian failure, learning difficulties) persist despite early diet correction.

Organ Systems

Pathway Steps

  1. galactose → galactose-1-phosphate — via galactokinase (GALK1). Galactokinase phosphorylates galactose (from lactose digestion). GALK1 deficiency is a milder galactosemia whose main feature is cataracts, from galactose diverted to galactitol by aldose reductase in the lens.
  2. galactose-1-phosphate → glucose-1-phosphate — via galactose-1-P uridyltransferase (GALT) — CLASSIC GALACTOSEMIA enzyme. GALT (galactose-1-phosphate uridyltransferase) deficiency is classic galactosemia — toxic galactose-1-phosphate accumulation causes liver failure, E. coli sepsis, and intellectual disability, managed by lifelong galactose/lactose restriction.

References