Substrate binding mechanism of Glu180-->Gln, Asp176-->Asn, and wild-type glucoamylases from Aspergillus niger

Biochemistry
U ChristensenB Svensson

Abstract

Glucoamylase (1,4-alpha-glucan glucohydrolase, EC 3.2.1.3) from Aspergillus, of which the 3D structure is known, releases beta-D-glucose from the non-reducing ends of starch and other related oligo and polysaccharides, cleaving the alpha-1,4-bond positioned between subsites 1 and 2 in the enzyme-substrate complex. The presteady and steady state kinetics of two of the existing mutants, Glu180-->Gln and Asp176-->Asn, are presented here. The kinetic results are analyzed according to two reaction models: One suggested previously [Olsen, K., Svensson, B., & Christensen, U. (1992) Eur. J. Biochem. 209, 777-784], which contains three consecutive steps of the reaction, and one generally accepted and used in calculations of subsite energies [Hiromi, K. (1970) Biochem. Biophys. Res. Commun. 40, 1-6], which assumes important non-productive binding and identical values of the intrinsic catalytic constant independent of the chain length of the substrate. It is found that glucoamylase shows kinetics in accordance with a consecutive three-step mechanism, in which the formation of the Michaelis complex occurs in two steps and is followed by a slow catalytic step and fast dissociation of the products with no accumulation of enzyme-product compl...Continue Reading

References

Jan 1, 1983·Molecular and Cellular Biochemistry·K HiromiA Tanaka

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Citations

Jan 11, 2001·Biochimica Et Biophysica Acta·J SauerB Svensson
Aug 17, 1999·Current Opinion in Biotechnology·C Ford
Oct 3, 2002·Protein Expression and Purification·Bjarne R NielsenTorben P Frandsen
Jun 29, 2000·Annual Review of Biochemistry·H D Ly, S G Withers
Dec 14, 1999·Bioscience, Biotechnology, and Biochemistry·A TanakaH Obata
Dec 29, 1998·Analytical Biochemistry·C SureshS Umesh-Kumar
Aug 28, 2009·Critical Reviews in Biotechnology·Pardeep Kumar, T Satyanarayana

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