The molecular configuration of B. α-amylase, which contains neither sulfhydryl nor disulfide linkages, was studied by the spectrophotometric titration, optical rotation measurements, as well as analysis of enzymatic activity in alkaline and urea solution. In alkaline pH region up to pH 11.5 about 30 per cent of all phenolic hydroxyl groups ionize almost freely, and the molecule might be expanded reversibly to some extent at upper limit of this region. The remainder of phenolic hydroxyl groups which are masked ionizes irreversibly only above pH 11.5, causing the unfolding of the molecule and the inactivation of enzyme. The enzyme is stable against relatively strong alkali, even though it has no disulfide linkages which stabilize the molecule. The unfolding of the molecular configuration and enzymatic inactivation is apparently irreversible. However, the regeneration of activity of urea denatured enzyme, except that of alkali denatured enzyme, is achieved by removing the denaturant by dialysis, or by lowering the denaturant concentration by dilution.
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Isemura et al. (1962) studied this question.