Amylose prepared from starch dispersed in 10M-urea, pH6.2, was found to be resistant to the action of β-amylase and phosphorylase, though it was degraded by α-amylase. Amylose isolated by conventional methods was similarly refractory after urea treatment, and was hydrolysed by β-amylase to the extent of 32-35%; it had no inhibitory effect towards β-amylase. The physical and chemical properties of the modified amylose were in general comparable with those of normal amylose with a β-amylolysis limit of 94-98%%. Starch and amylopectin were unaffected by urea treatment, i.e. the presence of amylopectin protected amylose against changes induced in it by urea. It is speculated that urea treatment “freezes” amylose molecules in a conformation that renders non-reducing termini inaccessible to the active site of the exo-enzymes. Such changes may limit the degradative action of β-amylase and phosphorylase.
