Enzymatic synthesis of neolactotetraosylceramide by the N-acetyllactosamine synthase of human serum.
A high galactosyltransferase activity with lactotriaosylceramide as acceptor has been found in human serums. The reaction requires UDP-galactose, Mn2+, and Triton X-100. It has a pH optimum of 6.0 and a Km for lactotriaosylceramide of 0.66 mM. On the basis of methylation analysis and susceptibility towards beta-galactosidase the reaction product has been identified as neolactotetraosylceramide. Lactotetraosylceramide formation was not observed. Evidence is presented that the serum enzymic activity can be attributed to N-acetyllactosamine synthase (EC 2.4.1.90). The beta 1 leads to 4-galactosyltransferase activities with lactotriaosylceramide as acceptor have been determined in different human sera. The activity is independent of ABO, p and Rh blood-group status. The enzyme is within a normal range in serums of cancer patients.
D000818:Animals; D001789:Blood Group Antigens; D055598:Chemical Phenomena; D002621:Chemistry; D005915:Globosides; D006026:Glycoside Hydrolases / Q000378:metabolism; D006028:Glycosphingolipids / Q000096:biosynthesis*; D006801:Humans; D007788:Lactose Synthase / Q000097:blood*; D007790:Lactosylceramides / Q000096:biosynthesis*; D009237:N-Acetyllactosamine Synthase / Q000097:blood*; D009369:Neoplasms / Q000097:blood / Q000201:enzymology; D011817:Rabbits; D013379:Substrate Specificity
D001789:Blood Group Antigens; D005915:Globosides; D006028:Glycosphingolipids; D007790:Lactosylceramides; C036363:paragloboside; D007788:Lactose Synthase; D009237:N-Acetyllactosamine Synthase; D006026:Glycoside Hydrolases