An α-amylase which produces maltohexaose as the main product from strach was found in the culture nitrate of Bacillus circulans G-6 which was isolated from soil and identified by the author.
The enzyme was purified by means of ammonium sulfate fractionation, DEAE-Sepharose column chromatography and Sephadex G-200 column chromatography. The purified enzyme was homogeneous on disc electrophoresis. The optimum pH and temperature of the enzyme were around pH 8.0 and around 60°C, respectively. The enzyme was stable in the range of pH 5-10. Metal ions such as Hg²⁺, Cu²⁺, Zn²⁺, Fe²⁺ and Co²⁺ inhibited the enzyme activity. The molecular weight was about 76, 000. The yield of maltohexaose from soluble starch of DE (dextrose equivalent^*) 1.8-12.6 was about 30%, and the combined action of the enzyme and pullulanase or isoamylase increased the yield of maltohexaose.

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