Necessity of Calcium for the Renaturation of Reduced Taka-amylase A

Abstract

Effect of calcium ion on the refolding of reduced Taka-amylase A has been investigated. Presence of calcium ion in the reoxidation mixture was found to be necessary for the correct refolding. Addition of calcium ion equivalent to the reduced enzyme in molar basis was sufficient for the maximum recovery of enzymatic activity. The amount coincides well with that of the calcium atom which is firmly and specifically bound in native Taka-amylase A. Seemingly the calcium ion is bound to the polypeptide of the reduced en-zyme, and exerts so strong directive effect that the correct refolding occurs preferentially. This phenomenon is interesting as an example in which renaturation of a conjugated protein is controlled by its non-protein cofactor.
The authors are gratefull to Sankyo Co., Ltd. for supplying “Taka-diastase Sankyo”, and to Dr. K. Hamaguchi and Mr. K. Yutani for their helpful discussions.