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Glycogen storage disease type IIIa (GSD IIIa) is an autosomal recessive disorder caused by deficiency of the glycogen-debranching enzyme (AGL). Recent studies of the AGL gene have revealed the prevalent mutations in North African Jewish and Caucasian populations, but whether these common mutations are present in other ethnic groups remains unclear. We have investigated eight Japanese GSD IIIa patients from seven families and identified seven mutations, including one splicing mutation (IVS14+1G→T) previously reported by us, together with six novel ones: a nonsense mutation (L124X), a splice site mutation (IVS29–1G→C), a 1-bp deletion (587delC), a 2-bp deletion (4216–4217delAG), a 1-bp insertion (2072–2073insA), and a 3-bp insertion (4735–4736insTAT). The last mutation results in insertion of a tyrosine residue at a putative glycogen-binding site, and the rest are predicted to cause synthesis of truncated proteins lacking the glycogen-binding site at the carboxyl terminal. Thirteen novel polymorphisms have also been revealed in this study: three amino acid substitutions (R387Q, G1115R, and E1343 K), one silent point mutation (L298L), one nucleotide change in the 5'-noncoding region, and eight nucleotide changes in introns. Haplotype analysis with combinations of these polymorphic markers showed L124X, IVS14+1G→T, and 4216–4217delAG to be on different haplotypes. These results demonstrate the importance of the integrity of the carboxy terminal domain in the AGL protein and the molecular heterogeneity of GSD IIIa in Japan. [ABSTRACT FROM AUTHOR]

HepG2 cells were examined for the presence of UDP-D-xylose:β-D-glucoside α-1,3-xylosyltransferase activity by using 2-[(2-pyridyl)amino]ethyl β-D-glucopyranoside (Glcβ-R) as a fluorogenic acceptor. UDP-D-xylose and the acceptor were incubated with the HepG2 microsomal fraction, and the enzymatic reaction mixture was analyzed by HPLC. Structural analysis of the fluorogenic product by α-D-xylosidase digestion, FAB-MS, and Smith degradation revealed that it was Xylα1-3Glcβ-R, thus demonstrating the existence of β-D-glucoside α-1,3-xylosyltransferase. A solubilization study of the enzyme from the microsomal fraction indicated that it differed from UDP-D-xylose:α-D-xyloside α-l,3-xylosyltransferase of the HepG2 microsomal fraction producing Xylα1-3Xylα1-3Glc-R′ [R′, (2-pyridyl)amino-] from UDP-D-xylose and Xylαl-3Glc-R′ [Minamida, S., Aoki, K., Natsuka, S., Omichi, K., Fukase, K., Kusumoto, S. & Hase, S. (1996) J. Biochem. (Tokyo) 120, 1002–1006]. The newly detected enzyme appears to be involved in the biosynthesis of the Xylαl-3Glcβ-Ser structure of glycoproteins such as human blood coagulation factors VII and IX. [ABSTRACT FROM AUTHOR]