The fine structural features of oyster glycogen, especially its mode o
f multiple branching, was investigated by repeated enzymic treatment w
ith beta-amylase and pullulanase, followed by the precise analysis of
the alpha-1,4-linked glucosyl unit-chains by high performance anion ex
change chromatography (HPAEC). The purified glycogen (average mol. wt
8.5x10(5), <(CL)over bar> 11) obtained by DMSO-extraction from fresh o
ysters (Crassostrea gigas) collected in February (a time when the oyst
ers are edible) showed a distribution of alpha-1,4-D-glucosyl unit-cha
ins, with degrees of polymerization (dp) in the range 2-35 (dp 6, domi
nant), as measured by HPAEC after complete enzymic debranching. The oy
ster glycogen was subjected to stepwise degradations with beta-amylase
and pullulanase, and this procedure was repeated until complete hydro
lysis was achieved (extent and degradation of 98% after five treatment
s). The yield of the limit dextrin formed at each trimming step and qu
antitative analysis of the unit-chain distributions indicated that the
oyster glycogen has a highly branched structure (A:B-chain, 0.7:1), i
nvolving five or six times interlinkings of the chains (B-chains). Ass
uming that B1 chain carrying only A-chains, attaches by alpha-1,6-bond
s to another B-chain (B2 chain), which in turn attaches to a B3-chain,
and so on, the molar ratios of the unit-chains (A, B1, B2-) of the de
xtrins during successive enzymic trimming showed that the ratio of A:B
1:B2:B3:B4:B5-chain was 34:25:11:5:5:1, confirming the multiple ramifi
ed molecule. In connection with the digestion of oyster glycogen in th
e mammalian digestive tract, the glycogen was hydrolyzed by salivary a
nd pancreatic alpha-amylase, and several branched maltosaccharides in
the digestion product were fractionated, and their structures determin
ed using HPAEC. (C) 1997 Elsevier Science Ltd.