Biologia, Bratislava, 57/Suppl. 11: 163-170, 2002.

ISSN 0006-3088 (Biologia).

 

Full Paper

Mechanism of porcine pancreatic a-amylase: Inhibition of amylose and maltopentaose hydrolysis by various inhibitors.

 

Veronique Desseaux1*, Roger Koukiekolo1, Yann Moreau2, Marius Santimone1 & Guy Marchis-Mouren1

1 IMRN, Institut Méditerraneen de Recherche en Nutrition, Faculte des Sciences et Technique de St Jerome, Universite d’Aix-Marseille, Av. Esc. Normandie-Niemen case 342, F-13397 Marseille cedex 20, France; fax : ++ 33 4 91 28 84 40, e-mail: veronique.desseaux@univ.u-3mrs.fr

2 IRD, Institut de Recherche pour le Developpement, Gamet c/o CEMAGREF BP 5095, F-34033 Montpellier cedex 1, France

* corresponding author

Received: February 6, 2002 / Accepted: April 18, 2002

 

Abstract

The effect of the pseudotetrasaccharide inhibitor acarbose, a-, b- and g-cyclodextrins and the Phaseolus protein inhibitor a-AI on amylose and maltopentaose porcine pancreatic a-amylase (PPA)-catalysed hydrolysis was studied. Statistical analysis of the kinetic data was performed. Acarbose is a strong inhibitor (K1i = 1.6 mM for amylose and 3 mM for maltopentaose). The inhibition is of the mixed noncompetitive type involving abortive complexes. a-, b- and g-Cyclodextrins are much weaker inhibitors (K1i = 7, 1.2 and 3 mM, respectively with amylose and 7, 2.5 and 3.1 mM, respectively for maltopentaose). The inhibition of amylose hydrolysis is competitive while the inhibition of maltopentaose hydrolysis is, as above, mixed noncompetitive. The Phaseolus protein a-AI is a strong inhibitor of both amylose and maltopentaose hydrolysis. However, the inhibition differs from the ones described above, in that a preincubation period of the inhibitor with PPA is required. However the same general equation applies and the inhibition is mixed noncompetitive. Aside from the inhibition of amylose hydrolysis by cyclodextrins, the other examples of inhibition, whatever the inhibitor used, are of the mixed noncompetitive type indicating that one (or two) secondary carbohydrate binding site(s) in addition to the active site participate(s) in the amylolytic process. X-ray studies of the crystallized amylase-inhibitor/substrate complex show secondary (accessory) carbohydrate binding sites in addition to the active site. These binding sites are very likely the same as those kinetically determined; they might play a role either at the substrate entrance or at the product exit and they might also participate in displacement of the amylose chain in the multiple attack mechanism.

 

Key words: porcine pancreatic a-amylase, inhibition kinetics, maltopentaose, acarbose, cyclodextrin, Phaseolus vulgaris.