Action of Pseudomonas isoamylase on various branched oligo and poly-saccharides.

Pseudomonas isoamylase (EC 3.2.1.68) hydrolyzes (1 linked to 6)-alpha-D-glucosidic linkages of amylopectin, glycogen, and various branched dextrins and oligosaccharides. The detailed structural requirements for the substrate are examined qualitatively and quantitatively in this paper, in comparison with the pullulanase of Klebsiella aerogenes. As with pullulanase, Ps. isoamylase is unable to cleave D-glucosyl stubs from branched saccharides. Ps. isoamylase differs from pullulanase in the following characteristics: (1) The favored substrates for Ps. isoamylase are higher-molecular-weight polysaccharides. Most of the branched oligosaccharides examined were hydrolyzed at a lower rate, 10% or less of the rate of hydrolysis of amylopectin. (2) Maltosyl branches are hydrolyzed off by Ps. isoamylase very slowly in comparison with maltotriosyl branches. (3) Ps. isoamylase requires a minimum of three D-glucose residues in the B- or C-chain.