Steady-state inhibitory kinetic studies on the ligand binding modes of Aspergillus niger glucoamylase. |
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Authors: | A Tanaka M Ohya T Yamamoto C Nakagawa T Tsuji K Senoo H Obata |
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Institution: | Faculty of Bioresources, Mie University, Japan. akiyoshi@bio.mie-u.ac.jp |
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Abstract: | Inhibitory activities of 1-deoxynojirimycin and gluconolactone on Aspergillus niger glucoamylase were studied in relation to the subsite structure of the enzyme. Although both of these inhibitors are considered to bind at subsite 1 of the enzyme active site, 1-deoxynojirimycin showed competitive type inhibition but gluconolactone was a mixed type (or noncompetitive type) inhibitor for the hydrolysis of p-nitrophenyl alpha-D-glucoside. The former type of inhibition suggested that the main binding mode of the substrate was productive, but the latter, nonproductive. A possible way of explaining these apparent inconsistent results is to assume that the main binding mode of the substrate is productive and gluconolactone forms a nonproductive ternary complex with the enzyme and the substrate. |
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