Multiple branching in glycogen and amylopectin

J. J. Marshall, W. J. Whelan

Research output: Contribution to journalArticle

51 Scopus citations

Abstract

The β-amylase limit dextrins of glycogen and amylopectin are completely debranched by joint action of isoamylase and pullulanase. Action of isoamylase alone results in incomplete debranching as a consequence of the inability of this enzyme to hydrolyze those A-chains that are two glucose units in length (half the total number of A-chains). From the reducing powers released by isoamylase acting (a) alone and (b) in conjunction with pullulanase, the relative numbers of A- (unsubstituted) and B- (substituted) chains in the β-dextrins, and therefore in the native polysaccharides themselves, can be calculated. Examination of a series of glycogens and amylopectins in this way showed that the ratio of A-chains: B-chains is markedly higher in amylopectins (1.5-2.6:1) than in glycogens (0.6-1.2:1). Glycogen typically contains A-chains and B-chains in approximately equal numbers; amylopectin typically contains approximately twice as many A-chains as B-chains. These polysaccharides therefore differ in degree of multiple branching as well as in average chain length. A consequence of these findings is that amylopectin cannot be formed in vivo by debranching of a glycogen precursor, as proposed by Erlander, since it is impossible to increase the A:B chain ratio by action of a debranching enzyme.

Original languageEnglish (US)
Pages (from-to)234-238
Number of pages5
JournalArchives of Biochemistry and Biophysics
Volume161
Issue number1
DOIs
StatePublished - Mar 1974

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

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