Galactosyltransferase mammary gland

Most of these reactions take place in the cystosol of the epithelial cells surrounding the alveoli of the mammary gland, but the final step, in which the galactosyltransferase is modified by a-lactalbumin, occurs... 

We have already seen in Section II,B that lactose is synthesized in the mammary gland through an enzyme, lactose synthase, which consists of two main components galactosyltransferase and a-lactalbumin. The latter acts as a specifier protein modifying the action of the galactosyltransferase. 

In lactating females, the mammary gland protein, aiactalbumin (which is activated hormonally in mothers shortly after birth) binds to galactosyltransferase and changes its specificity so that it catalyzes the synthesis of lactose (the major sugar of milk), as follows ... 

Fig. 30.6. Lactose synthesis. Lactose is a disaccharide composed of galactose and glucose. UDP-galactose for the synthesis of lactose in the mammary gland is usually formed from the epimerization of UDP-glucose. Lactose synthase attaches the anomeric carbon of the galactose to the C4 alcohol group of glucose to form a glycosidic bond. Lactose synthase is composed of a galactosyltransferase and a-lactalbumin, which is a regulatory subunit.

Rajput, B., Shaper, N.L. and Shaper, J.H. Transcriptional regulation of murine pi,4-galactosyltransferase in somatic cells. Analysis of a gene that serves both a housekeeping and a mammary gland-specific function. J. Biol. Chem. 1996, 27], 5131- 5142. 

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