Search

Two endo-beta-D-glucanases which act, respectively, on (1 leads to 3)-beta-D-glucans and barley beta-D-glucan have been isolated from malted barley, and purified by ion-exchange chromatography. The latter enzyme is highly specific for barley beta-D-glucan, and has no action on either (1 leads to 3)- or (1 leads to 4)-beta-D-glucans. It will also act on dyed barley-beta-D-glucan. Certain group-specific reagents inhibit the endo-barley-beta-D-glucanase and the endo-(1 leads to 3)-beta-D-glucanase to similar extents.

A limit dextrinase, free from contaminating carbohydrases, has been purified from malted sorghum flour. The enzyme readily hydrolysed alpha-limit dextrins having maltosyl or maltotriosyl side-chains, pullulan, and amylopectin beta-limit dextrin. Glycogen beta-limit dextrin and amylopectin were more slowly hydrolysed, the detection of the hydrolysis of amylopectin being dependent on enzyme concentration. No significant debranching of glycogen could be detected.

The limit dextrinases from ungerminated oats and rice have been purified, and their substrate specificity compared with a bacterial isoamylase preparation. Both cereal enzymes could hydrolyse (1 yields6)-alpha-D-glucosidic linkages in oligosaccharide alpha-dextrins, pullulan, amylopectin, and the beta-limit dextrins of amylopectin and glycogen. However, under comparable conditions, they were unable to attack glycogens.

A commercial enzyme preparation, of fungal origin, contained a mixture of beta-D-glucanases which were fractionated by ion-exchange chromatography to give a mixture of an endo-(1 leads to 4)- and an exo-(1 leads to 3)-beta-D-glucanase. These two enzymes were then separated by molecular-sieve chromatography on Sephadex G-150. The purified exo-(1 leads to 3)-beta-D-glucanase has a relatively high specificity for (1 leads to 3)-beta-D-glucosidic linkages, and has no action on lichenin.

Isoamylase has been prepared by affinity chromatography of a commercial enzyme-preparation from a strain of Cytophaga (also known as a Flavobacterium or Polyangium). The enzyme was not very stable, but the stability could be improved by calcium ions. The enzyme had a very low but significant activity on pullulan and on alpha-dextrins having maltosyl side-chains. This observation, which is contrary to previous reports, has been related to the specificity of isoamylase and other bacterial debranching-enzymes.

The rate of hydrolysis of amylopectin by three different limit dextrinase preparations is only about 15-23% of that of amylopectin beta-limit dextrin under similar conditions. On dilution of the enzymes there was no change in specificity. The factors controlling the specificity of the enzyme and the possible significance in vivo of the results are discussed.