Structure and stability of glucoamylase II from Aspergillus niger: A circular dichroism study.

Glucoamylase II (Ee 3.2.1.3) from Aspergillus niger bas 31%a-helix, 36% beta structure
and rest aperiodic structure at pH 4·8 as analysed by the method of Provencher and
Glockner (1981, Biochemistry, 20, 33). In the near ultra-violet circular dichroism spectrum the
enzyme exhibits peaks at 304, 289, 2.'12 and 257 nm and troughs at 285, 277 and 265 nm
respectively. The enzyme activity and structure showed greater stability at pH 4'8 than at
pH 7'0, were highly sensitive 10 alkaline pH but less sensitive to acid pH values. The enzyme
retained most of its catalytic activity and structure even on partial removal of carbohydrate
moieties by periodale treatment bul was less stable al higher temperatures and storage at 30 degree centigrade.
Reduction of the periodate treated enzyme did not reverse the loss of stability. Binding of the
synthetic substrate, p-nitrophenyl-a·D-glucoside, perturbed the environment around aromatic
amino acids and caused a decrease in the ordered structure.