Some physicochemical properties of the acid-stable α-amylase and the acid-unstable a-amylase, produced by Asp. niger simultaneously, were investigated comparing with each other. The molecular weights of the acid-stable α-amylase and the acid-unstable α-amylase were computed from sedimentation equilibrium as 58, 000 and 61, 000, respectively. And the molecular shapes were investigated by measuring sedimentation coefficient and intrinsic viscosity. The results indicated that these two α-amylases were similar in hydrodynamic properties and that they were prolate ellipsoids and poor hydrated proteins. But high frictional ratio of the acid-stable α-amylase suggested a certain degree of molecular asymmetry. Isoelectric points of the acid-stable α-amylase and the acid-unstable α-amylase were deter-mined as pH 3.44 and 3.70, respectively.

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