A study by means of lactone inhibition of the role of a “half-chair” glycosyl conformation at the active centre of amylolytic enzymes |
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Authors: | Elemér László János Holló Agoston Hoschke Géza Sárosi |
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Institution: | Department of Agricultural Chemical Technology, University of Technical Sciences, Budapest H-1521 Hungary |
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Abstract: | The kinetics of inhibition of porcine-pancreatic alpha amylase, sweet-potato beta amylase, and Aspergillus niger glucamylase enzymes have been studied by use of d-glucono-l,5-lactone and maltobiono-1,5-lactone as transition-state analogs. With d-glucono-1,5-lactone, alpha amylase can be inhibited, to a degree, non-competitively (Ki0.81mM,β≈e0.2), whereas with maltobionolactone, the inhibition is competitive (Ki10.31mM). The effect of beta amylase can be inhibited with maltobionolactone in a completely competitive way (KiO.11mM), whereas with d-gluconolactone the inhibition is very poor (Ki21mM). Glucoamylase cannot be inhibited with maltobionolactone, whereas with d-gluconic acid, a completely mixed inhibition way be observed (Ki1.3mM). The ratio of the binding affinity of the lactones, products, and substrates, permits the conclusion that ring distortion takes place in the transition state with all three enzymes. |
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