Enzymatic Synthesis of Neolactotetraosylceramide by the N-Acetyllactosamine Synthase of Human Serum

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Abstract
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 β‐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 β1→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.