Complex-type Asn-linked oligosaccharides do not always have the same number of branches, although there are normally from two to five. Each branch is formed by a specific N-acetylglucosaminyltransferase (GnT). N-Acetylglucosaminyltransferase-IV (GnT-IV) is essential in producing multiantennary sugar chains cooperatively with GnT-V. Much evidence has been accumulated which indicates the profound effect of multiantennary sugar chains on the physiological functions of bioactive glycoproteins. While there are many reports on the expression of GnT-V products related to tumorigenesis and organ differentiation, little information is available about when and where GnT-IV products are expressed. This is because of a lack of probes specific for GnT-IV products. However, the GnT-IV gene family is unique among GnTs for N-glycan biosynthesis. Although the biological meaning of each member is not well understood, GnT-IV may have functional roles which are no less important than those of GnT-V.
KeywordsRecombinant Human Erythropoietin Sugar Chain Acceptor Substrate Asialoglycoprotein Receptor Hepatoma Tissue
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