IngentaConnect On the mechanism of -amylase: Acarbose and cyclodextrin inhibitio...

Authors: Oudjeriouat, Naïma¹; Moreau, Yann²; Santimone, Marius¹; Svensson, Birte³; Marchis-Mouren, Guy¹; Desseaux, Véronique¹

Source: FEBS Journal, Volume 270, Number 19, October 2003 , pp. 3871-3879(9)

Publisher: Blackwell Publishing

Abstract:

Two inhibitors, acarbose and cyclodextrins (CD), were used to investigate the active site structure and function of barley α-amylase isozymes, AMY1 and AMY2. The hydrolysis of DP 4900-amylose, reduced (r) DP18-maltodextrin and maltoheptaose (catalysed by AMY1 and AMY2) was followed in the absence and in the presence of inhibitor. Without inhibitor, the highest activity was obtained with amylose, k_cat/K_m decreased 10³-fold using rDP18-maltodextrin and 10⁵ to 10⁶-fold using maltoheptaose as substrate. Acarbose is an uncompetitive inhibitor with inhibition constant (L_1i) for amylose and maltodextrin in the micromolar range. Acarbose did not bind to the active site of the enzyme, but to a secondary site to give an abortive ESI complex. Only AMY2 has a second secondary binding site corresponding to an ESI₂ complex. In contrast, acarbose is a mixed noncompetitive inhibitor of maltoheptaose hydrolysis. Consequently, in the presence of this oligosaccharide substrate, acarbose bound both to the active site and to a secondary binding site. α-CD inhibited the AMY1 and AMY2 catalysed hydrolysis of amylose, but was a very weak inhibitor compared to acarbose.β- and γ-CD are not inhibitors. These results are different from those obtained previously with PPA. However in AMY1, as already shown for amylases of animal and bacterial origin, in addition to the active site, one secondary carbohydrate binding site (s₁) was necessary for activity whereas two secondary sites (s₁ and s₂) were required for the AMY2 activity. The first secondary site in both AMY1 and AMY2 was only functional when substrate was bound in the active site. This appears to be a general feature of the α-amylase family.

Keywords: amylose; maltodextrin; acarbose; barley α-amylase; binding site

Document Type: Research article

DOI: 10.1046/j.1432-1033.2003.03733.x

Affiliations: 1: IMRN, Institut Méditerranéen de Recherche en Nutrition, Faculté des Sciences et Techniques de St Jérome, Université d'Aix-Marseille, France; 2: IRD, Institut de Recherche pour le Développement, UR081 Gamet c/o CEMAGREF Montpellier, France; 3: Carlsberg Laboratory, Department of Chemistry, Copenhagen Valby, Denmark

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On the mechanism of α-amylase: Acarbose and cyclodextrin inhibition of barley amylase isozymes