Lactose synthesis occurs only in the mammary glands, producing lactose (4-O-B-D-galactosylpyranosyl-a-D-glucopyranoside), the major sugar in milk. Lactose is created by joining two monosaccarides with a B1,4 glycosidic bond. Glucose is first converted to UDP-galactose via the enzyme galactose-1-phosphate uridylyltransferase. UDP-galactose is then transported into the Golgi by the UDP galactose translocator, an antiporter which uses facilitated transport to move UDP galactose into the Golgi and exports UMP. Once inside the Golgi, the UDP galactose and glucose (which moves into the golgi via the GLUT-1 transporter) become substrates for the lactose synthase enzyme complex, comprised of the enzymatic subunit, galactosyltransferase with its regulatory subunit, Alpha-lactalbumin. Lactose synthase creates lactose through bonding galactose from UDP to glucose through a glycosidic bond. Although GT is found in many tissues in the body, Alpha-lactalbumin is only found on the inner surface of the Golgi in the mammary glands, limiting lactose production to the mammaries.

Lactose Synthesis References