UDP-GlcNAc: BetaGal Beta-1,3-N-Acetylglucosaminyltransferase 1 (B3GNT1), i-Enzyme (iGnT)

  • Minoru Fukuda
Reference work entry


The majority of glycoproteins and glycolipids contain one N-acetyllactosamine unit. However, some of them contain more than one N-acetyllactosamine unit, and they are called poly-N-acetyllactosamines. Poly-N-acetyllactosamines are synthesized by addition of N-acetylglucosamine to galactose terminal of N-acetyllactosamine attached to glycoproteins and glycolipids. This enzyme is thus called N-acetyllactosamine extension enzyme. N-acetyllactosamine repeats are the epitope for i-antibody, which reacts with fetal and umbilical cord human erythrocytes (Fig. 25.1). After birth, the N-acetyllactosamine is extended and then branched to form Galβ1→4GlcNAcβ1→3 (Galβ1→4GlcNAcβ1→6) Galβ1→R, I-antigen. This i to I conversion takes place because of β-1,6-N-acetylglucosaminyltransferase newly appears. Because of this nature, I-antigen-forming enzyme is also called branching enzyme. Conversion of linear poly-N-acetylglucosamine to branched poly-N-acetyllactosamine is the first example of developmental antigen formation in carbohydrates (Fukuda et al. 1979).


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Copyright information

© Springer Japan 2014

Authors and Affiliations

  1. 1.Sanford-Burnham Medical Research InstituteLa JollaUSA

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