P4-Galactosyltransferase Family

For over 30 years it has been known that in the lactating mammary gland this enzyme can combine with the milk protein a-lactalbumin (a-LA) to form the laetose 

P4-GalT rV is a poorly acting enzyme and no activity could be detected with glycoprotein acceptors [172]. It has, however, notable activity with glycolipid acceptors and can support the synthesis of paragloboside. a-LA does not significantly induce the enzyme to act on Glc, but rather stimulates activity toward free GlcNAc [172]. 

P4-GalT VI has been identified as a lactosylceramide synthase [175]. Whether it acts on substrates other than glucosylceramide has not been determined. Finally, the p4-GalT involved in the first step of the synthesis of the GlcA(pi-3)Gal(pi-3)Gal(pi-4)Xyl core region of proteoglycans has recently been cloned and seems to be another member of this family [176, 195]. It is proposed to refer to this enzyme as p4-GalT VII. 

---