Identification and characterization of an UDP-Gal: N-acetyllactosaminide alpha-1,3-D-galactosyltransferase in calf thymus.
Calf thymus was found to contain a high activity of a galactosyltransferase, which transfers galactose from UDP-galactose to asialo-alpha 1-acid glycoprotein and N-acetyllactosamine. By means of competition and acceptor-specificity studies the enzyme could be distinguished from an N-acetylglucosaminide beta-1,4-galactosyltransferase and an N-acetylgalactosamine-protein beta-1,3-galactosyltransferase, which in addition occur in calf thymus, as well as from the blood-group-B-associated alpha-galactosyltransferase. Identification of the products revealed that the enzyme accomplishes an alpha 1 leads to 3 linkage resulting in a terminal Gal(alpha 1 leads to 3)Gal(beta 1 leads to 4)GlcNAc sequence. The enzyme is membrane-bound and is activated by Triton X-100. It shows optimal activity over a broad pH range (5.5-7.0) and has a pronounced requirement for Mn2+ ions (Km = 6.1 mM) for its action. It is suggested that the alpha-1,3-galactosyltransferase functions in the biosynthesis of calf thymocyte cell-surface glycoconjugates including glycoproteins.
D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D002855:Chromatography, Thin Layer; D005700:Galactosyltransferases / Q000145:classification / Q000302:isolation & purification*; D006023:Glycoproteins / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008745:Methylation; D008970:Molecular Weight; D013950:Thymus Gland / Q000201:enzymology*
D006023:Glycoproteins; D005700:Galactosyltransferases; C038887:N-acetyllactosamine alpha-D-galactosyltransferase