Immobilization of α-glucosidase on polystyrene plates: A practical application to α-amylase detection

α-Glucosidase is in high demand for applications involving the digestion of α-configured glycoside and saccharide substrates. Areas of application include industrial processing in food/feed and chemistry, as well as medicine and analytics. With an analytical application for assaying α-amylase in mind, we conducted a study on the immobilization of α-glucosidases from Bacillus stearothermophilus and Saccharomyces cerevisiae on support materials based on polystyrene and polymethacrylate. The carriers had nine different surface functional groups: none (plain material), carboxylate, sulfate, thiol, hydroxy, amine, sulfonyl chloride, epoxy, and PEG300. Based on preliminary results obtained with polymer beads, we selected the α-glucosidase from B. stearothermophilus and polystyrene plates with surface functional groups for detailed studies on enzyme immobilization. Carrier activity (A_c), immobilized enzyme effectiveness (ƞ), and reusability were evaluated depending on protein loading. Sulfonyl chloride (-SO₂Cl) showed efficient and stable immobilization (A_c up to 279 U/m² carrier; ƞ 58 %; A_c after 6 uses, 171 U/m² carrier). The α-glucosidase immobilized onto sulfonyl chloride-polystyrene carrier was used in an assay of α-amylase activity as a representative analytical application. 4-Nitrophenyl 4,6-ethylidene-α-D-maltoheptaoside was used as the chromogenic substrate in the α-amylase assay. The results indicated that the immobilized α-glucosidase was suitable for detecting α-amylase concentrations ranging from 0.1 µg/mL to 0.5 µg/mL (0.3 - 1.3 U/L as observed activities). Additionally, the results can be readily applied in a microtiter plate-based assay. Collectively, our results reveal the basic requirements for immobilizing α-glucosidase on polystyrene for the advancement of analytical assays.