Immobilization of the exo‐maltohexaohydrolase by the irradiation method

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Abstract
Exomaltohexaohydrolase (E.C.3.2.1.98) was immobilized by radiocopolymerization of some synthetic monomers which were mixed in various combinations. Irradiation was carried out while the mixture of monomers and enzymes was frozen in petroleum ether–dry-ice bath. Recovery of the immobilized enzyme was 44–75%. The optimum pH of the enzyme slightly shifted to the acidic side. The pH stability was improved remarkably by immobilization. The enzyme was stable retaining more than 90% of its original activity in the range pH 4–11. The optimum reaction temperature of the enzyme increased about 2°C. Heat stability was also improved by immobilization, and that the enzyme retained about 40% of its original activity after treatment at 75°C for 15 min. The immobilized enzyme was stable to the repeated use of 20 cycles. The Km value of the enzyme for short-chain amylose was almost the same as that of native enzyme. When soluble starch was used as the substrate, the Km, value of the enzyme was three times as large as that of native enzyme. Effects of various metal ions and inhibitors on the immobilized enzyme were also studied compared to the native enzyme.