The action of β-amylase on potato amylose

Abstract

I948 6. Exposure of amylose to hot water brings about changes even in the portion which does not retrograde. The blue value falls and fi-amylase action is incomplete. 7. Amylopectin was not so successfully purified, but fractional precipitation with ethanol freed it slightly from amylose which had escaped the first precipitation.

The selective hydrolysis of amylopectin and amylose by β-amylase

“…and a Lintner soluble starch prepared in our laboratory from potato starch were used. Amylose was prepared from potato starch by the thymol precipitation method of Bourne, Donnison, Haworth & Peat (1948), and amylopectin by cyclohexanol and thymol precipitation as described by Hopkins & Jelinek (1948). In some cases the amylopectin was preserved in solution, sterile. Starch and amylopectin were made into a cream with cold water, poured into boiling water and boiled with continuous mechanical stirring for 15 min.…”

“…Preparation of amylopectin. The purest preparation of amylopectin made in these laboratories was obtained by precipitation of potato starch paste with cyclohexanol followed 3 days later by thymol (Hopkins & Jelinek, 1948). It had been stored for 2 years and was difficult to get into solution unless finely ground, and all the precautions required in the preparation of starch paste were employed.…”

“…The starch residue was dispersed by boiling for 30 min., centrifuged to remove small amounts of residues, and the residual amylose (II) precipitated by thymol, leaving amylopectin II. The amylose preparations were purified and stored as described by Hopkins & Jelinek (1948). The amylopectins were kept in sterile solution, amylopectin II for 3 months and amylopectin III (prepared in the same way as II) for 6 days.…”

“…In view of the effects of salts on spectrometric measurements of iodine coloration, the concentration of buffer solutions was kept down to a 1% addition of 0. IM-acetate (for pH 4 6) and citrate-phosphate for pH 5-8 and 7. Progress of hydrolysis was followed and Michaelis constants were determined as described by Hopkins et al (1948).…”

Some Methods used for Characterising Fractions in Investigations on the Structure of Starch

“…This reaction is inhibited by the presence of a 1 : 6 linkage between glucose units which occurs at the point o f branching and shodd, therefore, be a positive and definite means of distinguishing between amylose and amylopectin. Some workers claim to have obtained complete conwersion o f arnylose to maltose by means of @-amylase (6,11,13). Others, working with a crystalline 8-amylase (1): find the reaction to cease at 7OOlo conversion (14,17).…”